Proceedings of the Indian Structural Steel Conference 2020 (Vol. 2)

In view of the rising development needs and maintaining the history and character of the places, conservation and restoration of Singapore’s built heritage has become significant when continuing to grow as a city of distinction. Regulated by the Urban Redevelopment Authority (URA) of Singapore, a strict set of guidelines are in place for a building which has been demarked for conservation when undergoing restoration or upgrading works to preserve the architectural features. Often, this poses a challenge for the engineers who need to ensure the structural safety of the heritage building constructed decades ago without adopting a formal building code, by complying with the modern building design codes. The paper focuses on the complex and innovative engineering approach adopted to upgrade a conserved building built in the 1950s to be able to withstand the increased design loads. The structural analysis of the single-storey building revealed that the existing reinforced concrete (RC) slabs, beams, columns and pad footings had insufficient capacities to meet the new demand due to the low concrete grade, corrosion of the existing reinforcing steel which resulted in spalling concrete and severe steel sectional losses. A hybrid method including RC jacketing, Tyfo® Fibrwrap® Systems proprietary Fibre Reinforced Polymer (FRP) Composite Systems and Tyfo® Corrosion Inhibitor Systems (CIS) were adopted to successfully restore and conserve the building as per the stipulated requirements.

Reinforced concrete (RC) deep beam is widely used in different types of engineering structures, viz. in high rise buildings, offshore structures and foundation pile caps, etc. Deep beam mostly failed under shear rather than flexure. Thus, shear strengthening of deep beam is of a challenging task. In the present paper, both experimental programme and a computer based finite element (FE) analysis of RC deep beam (GFRP strengthened\un-strengthened) is carried out. From both the investigations, the structural behaviour of deep beam in terms of strength enhancement and failure pattern is studied. Thereafter, a comparison has been carried out between those obtained experimental results and the finite element results to check the efficiency of the present numerical FE analysis. From both the studies, it is also evident that the advancement in numerical FE modelling can reduce the number of required test specimens for the resolution of a given problem, recognizing that experiments are time-consuming and expensive.

Carbon fiber reinforced polymer (CFRP) is becoming popular in construction and retrofitting of hollow steel sections due to its axial strength enhancement properties. This paper focuses on the axial behavior of CFRP-jacketed Circular Hollow Sections (CHS). CHS specimens of slenderness ratios—15 and 20, with varying configurations of CFRP laminates are studied. The specimens are subjected to axial static and axial cyclic loading, and the results are recorded. The CFRP-jacketed specimens exhibit an increase in axial strength up to 33.06% for axial static loading and 37.42% for axial cyclic loading. The stiffness of CFRP-reinforced specimens also shows an increase in value up to 65.55% and 42.74% for axial static and axial cyclic loading, respectively. The deformations and the modes of failure of the specimens under axial static and axial cyclic loading are also similar.

The concrete structure gets deteriorated with time due to its exposer to weather, dynamic loading, fatigue, and creep. So to maintain the strength and serviceability, retrofitting is needed. The steel plates were used previously for strengthening the existing structures, but steel plates tend to corrode with time, so nowadays FRP is the worldwide best solution as a material for strengthening the structure. Different FRP materials, such as a carbon-fiber-reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), aramid FRP (AFRP), and basalt FRP (BFRP), are available. Carbon FRP (CFRP) and glass FRP (GFRP) are used worldwide due to their lightweight and more tensile strength among all types of fiber. CFRP has more tensile strength as compared to GFRP but is uneconomical. To achieve the approximately same strength as that of CFRP, a multilayer of GFRP glued with epoxy can be used. This paper presents a state-of-the-art review of strengthening the RC beam-column junction under various loading based on experimental as well as computational simulation analysis done by various researchers in recent decades. Strengthening of a beam-column junction in static loading, seismic loading, and weak beam-strong column junction is evaluated experimentally and verified with finite element analysis using Abaqus, Ansys, etc. The ductile behavior of the RC beam-column joint is also reviewed.

Advancement in the material has led to a remarkable upsurge in the permissible stress level of materials. It is more so in the case of recently developed fiber-reinforced laminated composite materials. These panels are highly susceptible to buckle when they are exposed to in-plane loads, especially non-uniform loads. In most of the practical examples, FRP composite panels are provided with cutouts or openings to meet specific functional requirements, such as openings for entry, fuselage and some pipeline connections. These panels lead to premature failure depending on size of opening and loading conditions. Hence, it is essential to analyze the effect of in-plane edge load with cutouts. In this article, the effect of concentrated edge loads on buckling behavior of laminated panels with centrally placed circular cutouts has been considered. The plate is modeled by means of a 9-noded heterosis element by including the effect of shear deformation and rotary inertia. The effect of several parameters such as cutout size, the position of concentrated load, orientation of ply and panel thickness is included in this work to examine the buckling behavior of each parameter in detail.

Concrete filled steel tubes (CFSTs) are composite members in which concrete is encased within hollow steel tubes (HSTs). To understand the influence of the concrete core on the elastic local buckling stress and the axial strength of the steel tube, finite-element (FE) models of HST and CFST are developed using ABAQUS. From the FE analysis of CFST, it is evident that even for a diameter to thickness ratio (D/t) of 150 which is much higher than the (D/t) limit for slender members (D/t = 110), local buckling is not observed up to the ultimate load. This explains the reason for the highly conservative prediction of slender CFSTs by AISC 360-16. In addition, the yielding of the steel tube occurs before the peak strength of CFST is achieved, and the reduction in the load carrying capacity beyond peak load is due to the crushing of the core concrete. It is also observed that the axial strength of steel in CFSTs can be much lower than that predicted in the literature and codal provisions due to development of hoop stresses.

Composite structures are becoming a part of modern construction practice. Composite columns sections such as concrete filled tube (CFT), concrete filled double skinned tube (CFDST), and concrete encased steel (CES) have made the high-rise buildings and long bridges, reasonably safer and lighter. Newly evolved CFDST sections, where concrete sandwiched between two steel tubes, have shown improved performance under earthquake loading. The concrete infill enhances the load-carrying capacity and energy absorption and limits steel tube to get locally buckled. Furthermore, these sections provide high bending stiffness, better local and global stability, and enhanced post-peak behavior. Currently, in many countries like China and America, composite structures are constructed in a considerable extent. However, in India, utilization of composite columns is very limited because of lack of committed Indian standard stipulations. Acknowledging multifaceted nature in investigative answer for column element, utilization of load–moment (P-M) interaction curve plays a crucial role in design of composite column. Currently, available composite structure design codes predict the load–moment capacity based on either plastic design or strain compatibility design method. The present study aims to develop theoretical formulations for design of circular concrete filled double skinned tube (C-CFDST) composite column section using plastic method of design approach following Eurocode-4. Computer aid has been developed in Visual Studio 2019 with VB.net language based on proposed theoretical formulations to have a great advantage of computers in obtaining a solution for such complicated problems.

Any deviation from the expected shape and dimension of a steel member before loading is ascribed as an initial imperfection. They are formed in steel components during the manufacturing process, transportation, handling, fabrication etc. Traditionally, they are considered as a significant parameter in determining the actual capacity of slender steel members. International codes like AISC-360 and EC3 has prescribed column curves which includes the effect of initial imperfections in finding the global stability reduction factor for steel column design. A half-sine column profile with a maximum deviation of L/1500 and L/1000 are used as the initial global imperfections in the development of column curves as per AISC-360 and EC3, respectively. Similar design philosophy is adopted for concrete filled steel tubular long columns in AISC-360 and EC4. However, the experimental data available in literature for concrete filled steel tubular long columns is varying on comparison with code predictions. In this study, the axial compressive capacities of eighteen hollow and concrete filled steel tubular (CFST) long columns tested by the authors is correlated with the initial profile and magnitude of imperfections measured in the steel tubes before the commencement of tests. The axial test capacities of the specimens are around 30% higher than the code predictions. The initial double curvature (full-sine) profile of the steel tubes with very low magnitude in the bow imperfection has triggered concrete confinement in the CFST long columns, which lead to over-strength in the test specimens. Finite element model is developed using ABAQUS to comparatively study this phenomenon and the ultimate load. From this study, it is evident that the initial imperfections have higher significance on the axial behavior of CFST long columns than the hollow steel tubular columns.

This paper presents the behaviour and validation of finite-element modelling of double plate flat composite shear wall system subjected to static shear load with experimental results. A flat composite shear wall specimen was tested under static shear load. It is observed in the experiment that the failure of the composite shear wall is due to the buckling of cold-formed steel at the bottom of the compression side of the composite shear wall followed by cracks on the tension side of the exposed concrete surface. The experimental results are validated by numerical modelling of the composite shear wall using the finite-element package. A parametric study is carried out to find the effect of the number of shear studs (spacing of shear studs), yield strength of steel and compressive strength of concrete on the behaviour of the double flat plate composite shear wall. It is found that the load carrying capacity of walls is increased with decrease in spacing of shear studs.

This paper deals with the axial load carrying capacity of light gauge steel hollow circular section infilled with Nano concrete. Among the various infill materials, Nano silica is gaining attention in the concrete-filled steel tube (CFST) columns. The main objective of this paper is to study the axial load carrying capacity, relation between the steel and concrete interaction and also the characteristic of hollow steel column, plain and Nano silica infilled steel columns, load–deformation, load–axial strain and load–axial shortening of CFST columns. Nano silica was optimized as 2% in the Nano concrete based on the tests conducted. A total of 21 specimens were tested with a dimension of 50 mm diameter, 1.5 m length and the thickness of the steel tubes were taken as 1.2, 1.6 and 2.0 mm. Experiments were carried out with M30 grade of concrete, and finally, these experimental results are evaluated, and the experimental values are guide lines available validated with the existing codes such as Eurocode4 (EC4-2004), British code (BS5400-2005) and American code (ACI-1999).

Guidelines related to apportioning of steel–concrete composite sections to achieve maximum moment capacity and ductility are not available in present design codes. Study carried out in this paper is useful for apportioning of steel–concrete composite section. In present study, moment–curvature relationship of steel–concrete composite section considering its different parameters are explored. The considered parameters include cylindrical strength of concrete, effective flange width of concrete slab, distribution of area of steel section and confinement of concrete slab. From present study, it is found that for unconfined and confined concrete slab, moment capacity and curvature ductility of symmetric as well as un-symmetric section increase with increase in cylindrical strength of concrete and effective flange width of concrete slab. For same area of steel section, un-symmetric composite section with larger bottom flange area shows higher moment capacity and lower curvature ductility than symmetric composite section. Confinement in concrete slab enhances moment capacity and curvature ductility of symmetric and un-symmetric cross section.

Steel trusses supporting reinforced concrete floors and acting in composite action with it are efficient and functional arrangements for floor systems in buildings. If the truss can be made with cold-formed steel members connected by self-drilling screws the system becomes even more efficient. However, providing suitable shear connection between the truss and the slab becomes a challenge, and in this study, this was attempted by using cold-formed shear connectors connected to the top chord with self-drilling screws. The trusses were simply supported and tested under four-point bending. The truss carried higher loads due to mobilization of composite action with the concrete slab. Failure was ductile by loss of shear connector stiffness leading to local buckling of truss members. However, the truss can be used in lightly loaded floors of long spans as it can satisfy deflection limits. The test results are presented in the form of load-deformation curves and load-slip curves along with photographs showing the failure modes.

Concrete-filled tubular (CFT) column is a revolutionary combination of steel and concrete. It takes into account the respective merits and overcomes the limiting characteristics of these materials individually. This is being used worldwide from low rise to high multi-storeyed structures, but still its usage in India is limited due to the unavailability of standard specifications. Thus, a detailed study of EC4 and AISC 360-10 on axially loaded CFT column has been carried out, and their comparison has been made. Also, a database of more than 130 experiments from the literature has been created to assess the suitability of above standards for a large range of parameters. It is found that the predictions of EC4 are in good agreement with the experimental results, whereas the AISC 360-10 shows quite conservative results due to disregard of confinement effect of steel tube on concrete. The application range of EC4 can be extended to concrete of higher strength and to a higher diameter to thickness (D/t) ratio of steel tube. Based on the study carried out on the behaviour of various columns from literature, few refinements in the AISC 360-10 and EC4 are suggested incorporating the above discussed requirements which should be further studied.

This paper presents an experimental investigation on partially confined concrete-filled circular steel tubular (PCCFST) columns to explore the use of circular hollow section (CHS) configuration as partial inner confinement to the concrete-filled steel tubular (CFST) column. A total of four columns, three PCCFST and one CFST were tested under combined axial and cyclic lateral loadings. In this study, hysteretic behavior, flexural strength, ductility coefficient, energy dissipation capacity and failure mode of the PCCFST columns were investigated as a function of the height of inner CHS tube. Based on the experimental results, it was seen that the height of the inner CHS has evident influence on the energy dissipation capacity of the column. It has been found that, till 0.5D height of inner steel tube, there is no change in the hysteretic curve. For 1.5D height of inner steel tube, the flexural strength, ductility coefficient and energy dissipation capacity of CFST column were enhanced by 12.2%, 14% and 20.5%, respectively. This shows the structural viability of PCCFST column in the region particularly prone to seismic activity.

Composite structural members are recently used in major buildings since it possesses considerable load-carrying capacity and notable resistance toward fire and seismic forces. Steel concrete composite systems for structures are composed of concrete that interact with steel sections with the same system. This method is considered as a replacement for conventional method of construction. In a composite member, the steel section and concrete would oppose the extrinsic loading by its action of bonding and abrasion. The concrete encased around or infilled inside the steel specimen used is correlated that the merits of both materials are successfully used in the composite member. Encased columns are formed by I sections or built-up steel sections surrounded by concrete. Their integral behavior provides sufficient strength and stability to the structural system. This paper includes the review of the research work conducted on the buckling effects of encased column, concrete confinement, fire resistance, ductility behavior, and strength of encased column.

The primary aim of present research work is tuning the mechanical properties of wood and its composites applying mechanical annealing. The application of wood materials and its composites is gradually increasing in various fields, especially in the construction field due to its advantages such as lightweight, less processing cost and, renewable. For instance, magnetic wood composites are successfully applied as electromagnetic shielding, indoor electromagnetic wave absorption in electronic and military fields. Also, wood-plastic composites are using for moisture resistance, resistance to biological agents in biomedical filed. Moreover, recently, wood as a structural material is gaining significant attention to the research community; however, unswerving usage of wood obtained from trees is not strong as a building material; thus, it is necessary to modify its structure. There are various methods to enhance the strength of wood materials; one such method is mechanical annealing. In this work, the wood material is subjected to compressive stresses applying various monotonic load magnitudes P1, P2, and P3. Then mechanical properties are calculated using the 3-point bending test before and after mechanical annealing. Interestingly, central deflection decreased as the load increases. Finite element simulations performed to complement the experimental results. This analysis significantly helps in design of wood and its composites, and also wood can be used as an alternative material for structural steel.

This paper portrays the natural frequencies and mode shapes of composite circular plate being inspired from the construction of annual rings at stem of the tree. This bio-inspired concentric circular orientation of fibers unlike annual ring model can be utilized as structural components of engineering systems. Each layer of concentric circular fibers indicates the growth per annum. In present study, the simple concentric circular annual ring geometry is considered wherein the annual rings are idealized to construct each layer by graphite-fibers bonded together with epoxy resin in between the subsequent layers. Considering full clamped (FC) and half clamped (HC) boundary conditions, the first five natural frequencies are obtained and the corresponding mode shapes are plotted. The advantages of adopting these novel nature-inspired composites are compared with the conventional laminated composites.

Strengthening of different components of RC frame structure using fiber-reinforced polymer (FRP) is a very popular and convenient technique to withstand higher load. During last few decades, several researches have been carried out on reinforced concrete slab strengthened using different types of externally bonded FRP composites and adhesives. Various aspects of RC slab strengthened with externally bonded FRP have been reviewed in this paper. Though there is a huge advancement in the technology in the recent past, this topic has not been covered elaborately in previous studies. It covers subjects such as strengthening of punching and flexural strength for different types of slab, strengthening under different type of loading, use of different types of FRP, strengthening of slab with cutout, failure mode, FRP strain, crack load, ultimate load and ductility and assessment of extent of strengthening through finite element analysis. Furthermore, this paper reviews the debonding issues of externally bonded FRP sheet or strip. This paper finally concludes with the future scope of further research.

Following an earthquake, a building's capacity to withstand fire greatly diminishes, and the risk of fire also increases significantly. Although fire following an earthquake has a severe effect on structure, the subject has not been studied well. In this paper, the behaviour of concrete-filled steel tube (CFST) columns is presented under fire loading followed by an earthquake by using ABAQUS, a finite element-based analysis tool. The steps involved in numerical modelling were cyclic analysis and sequentially coupled thermal stress analysis. The output from the cyclic analysis was used as an input for the sequentially coupled thermal stress analysis. The results from the numerical analysis showed that the column with residual deformation failed early than the undamaged column.

Composite patch repair is a very effective and promising way to repair the cracked structure in order to increase their service life and structural integrity. There are a number of parameters which govern the performance of composite patch repair. In this work, symmetrical and un-symmetrical patch has been studied over the side crack on the aluminium aircraft panel. Contour integral technique has been implemented to model crack front discontinuity in the physical geometry. In order to check effectiveness of proposed computational model, benchmark problem has been solved with bonded patch structure. Further, few 3D patch repaired structures have been numerically solved to optimize patch repairing parameters like patch size, patch shape, adhesive material and patch configuration. In situ patch problems are analysed for cured thermal distribution in the patch repaired area over both symmetrical and unsymmetrical patch configuration. As a result of curing process, there is a variation in temperature throughout the repaired area; therefore, thermal residual stresses played a major role in structural integrity of repaired configuration. Numerical results are presented in the form of curing temperature contours, induced thermo-mechanical stress and fracture parameters like stress intensity factor (SIF). A decrease in SIF pattern has been observed in symmetrical patch as compared to unsymmetrical patch repair configuration. The patch curing temperature makes significant effect over SIF.

The ductility of structural elements is of prime importance to avoid brittle or catastrophic failure. Being strong in compression and weak in tension, concrete is very well known to be quasi-brittle material. Incorporating steel as reinforcing bars hence becomes crucial for making concrete worth using as a structural material. Furthermore, extensive research has been carried out worldwide on the use of short discrete fibers to enhance concrete’s tensile strength. Among several synthetic and metallic fibers, steel fibers emerge as an attractive option due to its high tensile strength and amazing crack-bridging potential. In this study, an experimental investigation was directed toward evaluating the effect of steel fibers when used along with traditional reinforcing bars on the ductility of reinforced concrete beams. For studying the effect of steel fibers on the ductility of reinforced concrete beams, a set of specimens was cast with varying percentages of steel fibers, i.e., 0, 0.5, 1, and 1.5%. The specimens were tested under three-point bending, and the load–deflection profiles were obtained for each case. The ductility index and flexural toughness for each case were determined using load–deflection profiles. It has been found that the presence of steel fibers enhances the ductility and flexural toughness of reinforced concrete beams significantly which was evident from its crack arresting potential leading to larger post-peak load deformations.

Composites are extensively used in various fields such as civil, aerospace, naval due to their high specific stiffness and strength. These properties are adversely affected due to damage. For damage detection, vibration-based methods are generally used which use modal parameters, i.e. modal frequencies, mode shapes and modal damping ratios. These modal parameters depend on the physical properties of the system, i.e. mass, stiffness and damping. Among these properties, damping is the most sensitive to damage. Therefore, the occurrence of damage should be sensed through changes in damping. Further, in order to localize the damage, a support model for damping is needed to spatially isolate the origin of the changes. Unfortunately, damping depends on numerous known and unknown physical phenomena that makes it difficult to model or estimate. In this study, first variation of modal damping ratios with damage in a composite column has been shown. Then, a new model of damping, called mode specific damping, is proposed. The performance has been checked through numerical simulations and compared with the Rayleigh model of damping.

Due to the gradual increase in axial load on the rectangular concrete-filled steel tube (CFST) column, initially, the steel tube and concrete core remain in contact all around; however, at higher loads, a gap between steel tube and concrete core is developed along the periphery of column except at corners. This gap leads to local buckling of steel tube, and as a consequence, the confinement effect to concrete is lost, and it is known as one of the major imperfection in CFST. This paper aims to study the effect of aspect ratio of column section and thickness of steel tube on imperfection. In this paper, three aspect ratios, namely 1.0, 1.25 and 1.5, have been considered while the thickness of the tube is varied from 2 to 4 mm at the interval of 1 mm. For the column with various aspect ratios and tube thickness, the variation of imperfection with axial load has been plotted in terms of the non-dimensional parameter denoted as gap ratio. For the column with rectangular cross section, the gap ratio at any face of the column is defined as the ratio of the gap and the length of that face. For the three-dimensional finite-element analysis of CFST using the ABAQUS, the steel tube and concrete core have been discretized into shell and solid elements, respectively, and the contact between the inner side of steel tube and the surface of the concrete core has been considered rough, and the friction coefficient is taken as 0.25. Based on the numerical study, it has been concluded that the axial load carrying capacity of the rectangular CFST column is reduced significantly with an increase in imperfection.

Concrete filled steel tube (CFST) columns have been widely used in structures largely subjected to compression such as high-rise buildings. To achieve taller constructions, engineers have improved CFST columns performance by applying high-strength materials to make the columns slender. Although the current standards [1, 2, 4] have taken CFST columns into practice, there are restrictions in the material strength and the section slenderness. To solve the problem, this paper presents a numerical examination of CFST columns fabricated from high-strength materials as well as slender sections under axial compression. For verification, a finite element (FE) model, taking into account the initial local imperfection, residual stress on a tube, the confinement effect of filled concrete and the buckling and post-buckling behavior of steel, was developed for CFST columns. Ultimate strengths obtained from numerical analysis were compared with practical code and experimental results to verify its reliable prediction. A parametric study of CFST columns with different concrete compressive strengths f′c, steel yield stresses fy and the width to thickness ratios B/t was also presented in the paper.

The influences of critical parameters affecting the long-term behaviour of prestressed concrete bridge with corrugated steel webs (PCBCSW) have been presented in this paper. A calibrated finite element numerical model was used to conduct a detailed parametric study. A total of eleven critical parameters were comprehensively studied using age-adjusted elasticity method (AAEM) to investigate their influence on the serviceability aspect of PCBCSW. Due to large shear deformation and negligible axial stiffness of corrugated steel webs, the Euler–Bernoulli and Timoshenko beam theories are not valid for this type of bridge, thus, the sandwich beam model proposed by Chen [5] was extended by Pandey [11] by duly considering the concrete creep and shrinkage as well as tendon relaxation models of different international codes. It has been found that the long-term deflection of PCBCSW was larger than the identical bridge with flat steel web, and comparable to those with the concrete web. However, the long-term prestress loss of PCBCSW was similar to those of conventional bridges.

Module concept construction, common in offshore projects, is one of the most advanced forms of construction approach currently being implemented in large scale on various onshore Oil and Gas and Chemical projects. The concept involves fabrication, assembly and pre-commissioning at offsite location (commonly known as Module Fabrication yard) where modularized process blocks are constructed with 95% steel and piping, 85% of electrical and 95% instruments on Module. Modules, once fabricated at Module Fabrication Yard, are transported to the site through barge (marine transportation, wherever applicable). Modules are loaded onto/off loaded from barge using Self-Propelled Module Transporter (SPMT). Once modules are offloaded, they are transported to the site thru SPMT for “setting procedure” where modules are rested on pedestal and “anchored”. This paper discusses on various methods of Module anchoring which may vary based on “Module type”, “site environment condition”, “constructability preferences” highlighting design assumptions, challenges (constructability, if any).

The increase in urbanization has led to the depletion of natural materials and increase in demolition of old structures. By suitably reusing the demolition waste materials, the demand for natural resources can be reduced. This paper aims to find mechanical properties of pumpable concrete made by partially replacing the natural aggregates with recycled concrete aggregates. The study was based on a pumpable M20 grade concrete mix. The tests were conducted on three types of mixes with 0, 25 and 50% of recycled aggregate concrete. It was observed that the compressive, tensile and flexural strength of pumpable concrete made with recycled aggregate showed improved compressive and tensile strengths.

The use of Steel-Reinforced Concrete (SRC) columns in regions of high seismic intensity has been on the rise in the recent decades. SRC columns offer notable improvements in the axial load-carrying capacity, lateral ductility and moment-resisting capacity over conventional reinforced concrete (RC) columns. The presence of the encased structural steel enhances the lateral deformation capacity of the column, while the exterior RC section prevents the encased steel from weathering. The current study is focused on performing an experimental investigation to assess the level of enhancement in the lateral ductility of the SRC columns over their RC counterpart. Two test specimens, one each of SRC and RC sections, were cast together and tested in the laboratory under fully reversed lateral cyclic displacements. The SRC column was designed using the provisions of Euro Code 4 for encased structural components, while the RC section was designed according to IS 456. The materials used in the specimens were M30 grade concrete and Fe500 grade steel for the longitudinal bars. Rolled steel section ISMB100 was adopted as the encased structural steel in the SRC specimen. The transverse reinforcement provided in accordance to IS 13920 with ductile detailing was maintained at the same percentage for both the specimens. The hysteresis response, lateral ductility, energy dissipation and moment contributions of steel and RC sections of the SRC column specimen were compared with those obtained for the RC section. For the same cross-sectional dimensions of the concrete, the level of improvement in the lateral ductility of the SRC column over the RC specimen is compared. From the findings of this study, it was observed that the presence of the encased steel significantly improved the lateral ductility, while the lateral capacity was 50% higher than that of the RC specimen. In terms of energy dissipation potential, the SRC column dissipated 2.5 times more energy than the RC column.

This paper presents the numerical validation of experiments’ transfer columns in hybrid structures with steel-reinforced concrete (SRC) columns in some stories while having reinforced concrete (RC) columns in the others. These hybrid structures may be subjected to localised story failure mechanism in an earthquake if they are not detailed properly. A numerical validation was carried in the ABAQUS software package. The parameters from the experiments were input in the software to get the backbone curve that would match with the experimental results. Once validation is complete, this model can be further used for conducting a parametric study.

Braces have been considered as the most desirable choice among the engineers as earthquake- and wind-resistant elements for the construction of steel-framed structures, whenever they are acceptable from the architectural point of view. The major drawback of conventional bracing is that it loses strength under compression due to buckling. Braces normally have slip-type hysteresis, and because of this, they cannot give suitable energy absorption. Buckling-restrained brace (BRB) is specially designed to restraint global buckling, and the pressure member is expected to yield before buckling. BRB is designed on a very simple concept which is to restrain the buckling behavior of the brace so that it perform the same behavior in tension as well as compression. As a result, BRB shows stable and nearly symmetrical characteristic. BRBs are emerging in these decades as an innovative and economical solution for the energy dissipation in the earthquake- and wind-resistant construction of steel-framed buildings. This paper presents a brief summary on the development of the unbonded braces and discusses the basic history, concept and applications of BRBs. Various configurations and the buckling behavior of the brace under different buckling modes are presented. The stability criteria for different failure modes are considered. It was found that the torsional buckling is the most critical mode for stability of the brace. Limitations of the brace are also discussed in brief.

The intent of this paper is to highlight the impact of developments in Transportation philosophies of modular structures as the project phases into advanced stages. The design parameters and logistics information get more refined when logistics contractor starts developing execution philosophy for the transportation of modules. It becomes more important that the mitigation measures are there in place to minimize effect on cost and schedule of the project. Modes of transportation discussed in this document are land and sea transportation for a large modularization project. For land transportation of modules, propelled module transporters (PMT)/self-propelled module transporters (SPMT) trailers were used. Mechanical properties of these trailers were defined in the beginning of the project. Modules were transported through water using barges/vessels. Sea accelerations were provided by logistics contractor for analysis and design of modular structures. The modules were fixed on barges/vessels with the help of sea fasteners. Sea fasteners and bulkhead capacities were also provided by logistics contractor. Module support reactions were then checked against these capacities. There was wide range of parameters which had an impact on the design of modules. It was important to mitigate them with effective and efficient solutions since fabrication was at advanced stage. Some of the revised parameters were sea accelerations’ coefficients, capacities of vessel/barges, capacities of SPMT/PMT, supporting configurations, etc. Various methods had been employed to screen the changes that were not having any detrimental impact on design of a structure. Also, several re-evaluation methods to mitigate the changes impacting the design were implemented.

The concrete-filled steel tube (CFST) is a composite member consisting of a steel tube and concrete infill. CFST combines the advantages of both steel and concrete member as they are placed concentrically. Circular CFST columns show better performance compared to square one, as they provide more confinement to concrete infill. But the application of circular CFST columns is limited, due to the difficulties in assembling the connection. Split bolt assembly avoids the complications in the circular CFST column connections and improves the efficiency of the joint compared to straight bolt assembly. Split bolt assembly allows the intersection of through bolts at the same level. In this work, the seismic response of an exterior semi-rigid stiffened extended endplate connection between circular CFST column and I-beam with split bolt assembly is studied under displacement-controlled cyclic loading. The numerical study was conducted to investigate the influence of axial load level and split bolt angle on the joint behaviour. Initial stiffness of joint increases with increase in axial load level but has negligible effect on moment capacity of the joint.

The behaviour of welded beam-to-column joints has widely been studied around the world in recent times as they are predominantly used in the construction of modern steel structures. Basically, the joint consists of an I-section as the beam, while a square hollow section as a column. There has been a dearth of literature on studies pertaining to the behaviour of such welded joints exposed to corrodants and cyclic loads. This served as an impetus to carry out experimental studies to evaluate the behaviour of welded steel beam-to-column joints that were subjected to accelerated corrosion and cyclic loading for the purpose of evaluation for seismic applications. The welded zone was corroded to the extent of causing a loss of 10% to the weight of the steel structure by applying a current of 18A. Sixteen loading cycles conforming to the seismic protocol load were applied to the beam. It was observed that the corroded welded joint failed at a lower load. The unequal distribution of the stresses and the plastic deformation at the corroded welded zone lead to the brittle fracture and ultimately to the failure of the joint.

This paper presents ductility-based seismic design approach for design of steel knee-braced moment frames (KBMF) and influence of ductility in the design process. Knee-braced moment frame is a hybrid energy dissipating frame which has combined characteristics of moment-resisting frames (MRF) and concentrically braced frames (CBF). In the proposed ductility-based seismic design approach, target displacement ductility ratio and target yield mechanism are the design criteria and the inelastic behaviour of the structure has been incorporated into the design process. A KBMF is designed using Indian Standard (IS) codes and three KBMFs are designed using the ductility-based seismic design approach for different target drifts and ductility conditions. Nonlinear static pushover analysis (NSPA) and nonlinear time history analysis (NTHA) are conducted to assess the effectiveness and study the responses of the frames under strong ground motions. The analytical test results show that the ductility-based seismic design approach produces frames with desirable and predictable structural responses.

This paper presents prequalifying criteria for hollow structural steel [HSS] truss connections. The criteria were derived based on the parametric study on T, Y, X, N and K type hollow structural steel truss connections. The parametric study was undertaken with reference to the recommendation of CIDECT design guide-3. The more influencing geometric parameters taken in this study were the ratio of brace width to chord width (β parameter), ratio of brace thickness to chord thickness (τ parameter), chord and brace slenderness values, chord and brace aspect ratios. An experimental investigation on welded T and X type truss connections was conducted to validate the prequalifying criteria which were obtained through the parametric study on these connections. The most influencing geometric parameter found in this experimental validation was the ratio of brace width to chord width. The prime objective of this prequalifying criteria is that it qualifies the HSS truss connection such that at its ultimate it governs the chord face plastification connection failure.

This paper analytically and numerically verifies the new design approach for cold-formed steel connections. The need of an easy and rapid construction of moment-resisting frames in cold-formed steel resulted in the screwed connections which are good in taking bearing and shearing forces. The closed cold-formed rectangular box sections are used as the main frame member. The connection idea is to symmetrically distribute the beam moments to column moments through the gusset plates which are screw fastened to the structural members. To begin with, the structural members are sized based on the structural loading. The optimum shape of the gusset plate was found based on the numerical formulations. The size of the gusset plates is formulated based on the beam and column sizes, possibility of assembling the required number of screws and also on the aesthetic sense. The thickness of the gusset plates is arrived based on the numerical simulations by modelling the screws as ties, and the research has progressed towards formulating the expressions for the minimum thickness of the gusset plates based on the moments. The availability of the sheets in the market and also the possible drilling thickness of self-drilling screw also affects the thickness of gusset plates for the practical works.

The idea of this paper is to critically review the various finite element modelling methods of screw connections in cold-formed steel. To have a detailed study, the finite element modelling of gusset plates with screws as the fastener has been taken. In the real model, the screws are subjected to bearing, shear and pullout forces. The various methodologies for modelling screw connections include tie constraint model, spring model and screw solid model with interactions. The modelling procedure, assumptions, merits and demerits of each finite element model are deeply studied. In the tie constraint model, the screws are modelled as ties which connects the two adjacent nodes. In this model, the behaviour of screws cannot be studied and are intended for studying the behaviour of connecting elements treating the screws as rigid. The spring model is an advanced model which accounts the bearing, shearing and pullout strengths of the screws which has to be programmed based on the experimental results. The more realistic one is the real solid modelling of screws in the connections. This numerical analysis does not need any input data’s other than the material properties. Even the model is computationally time consuming, the results give accurate screw stresses at the element level.

Fasteners are the backbone of steel construction industries. Various researches are being done on the different types of connectors. Self-tapping screws are one fastener used widely in cold-formed steel frame construction industries. Self-tapping screws are designed to cut their hole as it is screwed into the materials. This study presents an experimental investigation on static behaviour of self-tapping screw subjected to shear by varying the orientation, number of screws and thickness of material on which it is driven. In this experiment, two plates were connected by the self-tapping screw in a single lap connection. The tensile force was applied on the plates so that the screws were made to undergo shear failure. The group effect of screws and the reduction factor adopted in multiple screw arrangements have been studied. The stiffness of the connectors was analysed. The connection with more screws and thicker plates was found to be stiffer.

Cold-formed steel (CFS) columns are increasingly used in structures for their high strength-to-weight ratio. CFS tubular columns of square, rectangular, circular, and various innovative cross-sections are being experimented worldwide. Also, spirally welded (SW) pipes, which have a massive usage in pipeline industry, have their room of experimentation as a column. Longitudinal welded columns necessarily require steel sheets/coils of certain height to avoid coil girth welding, but available sizes are limited. Spiral turning and welding of steel sheet allow manufacturing of different sized columns with the same width of the sheet. Unlike longitudinal pipes, continuous and very long spiral-welded columns can be manufactured using compact coil strips. In spiral welding, with the same width of the sheet by varying the revolving radius small to large diameter columns can be produced. Also by varying the pitch, with the same length of the sheet, columns of different lengths can be produced. In this paper, SW columns with varying pitch and L/D ratios are modeled and analyzed using finite element program ABAQUS and their buckling behavior is studied.

Need for a high-speed rail demands the continuous welded rail (CWR) to be continued on the bridge to make a smooth track eliminating special expansion joints (SEJs). Braking load is an important consideration for the design of railway bridges. Being a slender steel structure, CWR is prone to buckling and fracture due to compressive and tensile rail stresses, respectively. Track bridge interaction (TBI) phenomenon results in additional rail stress, which varies along the track–bridge portion of CWR. This paper investigates TBI due to braking load. Effect of braking load on the rail stress and the longitudinal support reaction of the bridge pier have been investigated. A numerical model developed for track–bridge interaction in SAP2000 is extended to study the effect of braking load in the presence of ballasted CWR track. UIC 774-3R Code guidelines are followed while modeling the phenomenon. When compared to a bridge with special expansion joints, a significant portion of the braking load is dissipated in the approach zone of the bridge as a result of track–bridge interaction for all span lengths. The longitudinal support reaction at the fixed end pier of the bridge support is also affected significantly.

Damage or distress caused due to earthquakes need to be retrofitted to enhance the load carrying capacity of distressed structural members. This study focuses on the behavior of a L-shaped Flat slab structure having 10 × 10 × 2 bays in plan and 9 stories to seismic loads using ETABS. One set of models for study are carried out with steel X-bracings between the columns vertically at various locations in the plan of the structure. A second set of models for study are carried out by providing steel plate bonded columns at all stories for different columns in the plan of the structure. The performance of the structural models in earthquake and comparison with that of reference model without any lateral load resisting system is studied. The comparative study between the two sets of models is carried out to check the performance of steel X-bracings as compared to steel plate bonded columns.

The present study focused on numerical investigation on beam-column end plate connection provided with cellular beam. If the beam possesses openings in the web portion it is referred as cellular beam. The perforation in the cellular beam tries to shift the position of plastic hinge away from the beam-column connection under cyclic load conditions. The finite element analysis was carried out for cellular beam provided with circular opening in the web portion. The radius of web opening was varied as 30, 40, 50, 60 mm in order to assess the performance of the connection in terms of rotational stiffness, failure mode etc.. The moment-rotation behaviour of the connection was analysed under static and cyclic load conditions. The loading history for cyclic load condition was given as per FEMA 350 guidelines. While increasing the radius of web opening of cellular beam, the moment capacity was found to be increased. The plastic region is extended before failure which was observed from the moment-rotation behaviour of beam-column end plate connection under consideration.

Compared with conventional onsite construction, modular construction provides significant benefits such as faster and safer manufacturing, better quality control, and less environmental impact due to allowing up to 95% of a building to be prefabricated in a controlled factory environment. These benefits can be maximised in high-rise buildings due to the increased number of repeated modules. However, most of the success stories of adopting modular construction are limited to low-rise buildings due to a lack of a joining technique which can ensure lateral resistance, structural integrity, overall stability, and robustness of the whole modular building. This paper presents a numerical study of a novel joining technique which not only enables easy and quick installation, but also provides adequate strength and stiffness for use in modular tall buildings. A detailed finite element (FE) model is developed in ABAQUS to simulate the complex behaviour and failure mode of the connector. It is also verified with available experimental results. A parametric study is then performed to examine the effects of a wide range of geometric and material parameters on the behaviour of the connector.

Mankind is facing significant burden due to production of large quantities of construction and demolition waste. Therefore, new approaches in design and construction need to be found to increase recycling and reuse rates—use of reusable joints will contribute to an integral approach in construction. This paper focuses on reuse of steel joints which promotes the reduction in carbon emissions. It gives an overview of the advantages of the joint and challenges and provides recommendations. It also gives examples of successful applications with an overview of possible environmental savings and introduction of a new joint with its technical aspects as well as its merits and demerits over conventional joints. Experiments are performed to assess the structural characteristics and ultimate capacity of the connection. Physical and chemical tests are conducted on the reused steel and further analysis of channel sections is done using STAADPRO and the simulation of the whole assembly is done through Ansys to assess its behavior. FEM analysis is conducted on the connection joint to know the stress concentration and deformation in the joint. The connection shows maximum deformation of 31 mm at 400 kN load on the beam and maximum shear stress of 1778.9 Mpa at load applied much part of the connection shows shear stress of 290 Mpa. It is clear that for 400 kN load at beam end forming 160 kN-m moment, the vertical plates in the joint are deformed. Moreover, the plates in the center joint plate’s contribution to the load transfer mechanism is higher than the beam plates and equivalent strain in the connection. It is found that through proper design and detailing the reused joint will behave as per the design. Study also carried out to investigate the parameters that influence the stiffness, strength and rotation capacity of modular block shear connection. The joint is also validated for reusability through various parameters like elastic behavior, damages and traceability. It can be concluded that the material is totally fit for reuse based on the results obtained from chemical test and tensile test which satisfies the IS codes. Staadpro analysis and FEM analysis gives us the load carrying capacity of the joint and stress concentrations for testing purposes.