Stability and Failure of High Performance Composite Structures

Two-dimensional exact free vibration solution for functionally graded plates in cylindrical bending is provided in the present study. Exponential distribution of material properties across the thickness is considered and plane strain condition is assumed to reduce the three dimensional problem of plate bending to a two dimensional elasticity problem. Exact solutions for linearly elastic simply (diaphragm) supported and rectangular plates based on two dimensional elasticity theory, are derived. Navier’s solution technique along with power series method is used to find the natural frequencies. The assumed displacement field identically satisfies all the boundary conditions. Numerical results for frequencies are provided for exponentially graded thick and thin plates for various material gradations. Further, the present formulation is extended to static analysis of functionally graded plate under sinusoidal load.

In conventional reinforced concrete structures temporary formwork supports the wet concrete and the reinforcement during casting. The temporary formworks are usually made up of steel or wood are used to support fresh concrete during the casting and curing stage of concrete. They are removed after the concrete sets. An alternative to this method is the use of Stay-in-Place (SiP) forms. When they are structurally integrated with concrete, they hold the fresh concrete and acts as reinforcement to the system once the concrete is set. Thus, the development of competent bond strength between concrete and SiP form is imperative for their composite action. Fibre Reinforced Polymers (FRPs) have high resistance to corrosion, low self-weight, and high tensile strength. They have evolved as an alternative material for the construction industry with the strategic application of SiP. FRP SiP formworks are designed to act as a support for casting concrete and as a tension reinforcement when the concrete is cured. For composite action between the formwork and concrete, a proper bond between them is essential. This chapter presents state- of- art about FRP SiP formwork. It also presents a feasibility study in which an FRP plank was used as a SIP form serving as formwork during the wet stage and as reinforcement during the hardened stage. An experimental investigation was carried out through shear and flexure tests. A feasibility study in which a pultruded FRP plank was used as SiP form serving as formwork during the wet stage and as reinforcement during the hardened stage is presented in this paper. In shear tests, two different bond mechanisms, aggregate bonding, and adhesive bond were investigated using three different adhesives. Two different novel shear experimental setups were prepared to evaluate the bond. The load capacities and failure modes were examined. The experimental results show that the types of adhesive have a significant impact on the bond. In flexural testing, cyclic four-point bending tests were conducted on FRP SiP beams (with and without bond treatment) and conventional steel-reinforced beams to evaluate the load-carrying capacity and failure modes of the proposed hybrid beam. FRP-SiP beams failed at higher load and a higher deflection compared to conventional steel reinforced specimens. Thus, the present investigation affirms the feasibility of using FRP plank as SiP formwork.

When lateral and direct shear loads arise on precast concrete sandwich panels, the structural response depends on the ability of the panel to develop composite action. The wythe’s span and thickness, concrete mix constituents and strength, insulation and nature of the shear connectors all play a significant role in determining the load capacity and failure modes. This chapter will report on thermally conductive and non-conductive shear connectors and how they interact with the wythes and insulation in providing load resistance to both flexural and direct shear loading. In particular, the post-cracking behaviour prior to pull-out, shear or buckling failure is observed to vary considerably and needs to be understood in order to successfully design systems that are fit for purpose.

Composite hollow cylindrical tubes can provide superior design advantages in engineering structures due to their geometric versatility added with reduced weight. However, the response of such components especially failure prediction under combined, compressive, and torsional loading poses a long-standing challenge for the structural engineering community. With the advancement of automated fibre placement (AFP), thermoplastic tubular components can be manufactured accurately at a faster rate to optimize production efficiency. Moreover, the discontinuities such as cut-outs for inlets and service openings are often included in the design of composite structures, which can experience strength reduction along the process. This chapter presents the numerical analysis and experimental demonstration of thermoplastic Carbon Fibre-PEEK composite (CF-PEEK) tubes including cut-outs under simultaneous compression and torsional loading. A set of thermoplastic tubes with different sizes (length to diameter ratio) and stack up sequences were manufactured using a hot gas torch (HGT) assisted fibre placement machine. The specimens then were tested using a servo-hydraulic testing machine capable of applying compression as well as torsional loading both independently and concurrently. The experimental results were compared with numerical simulation carried out using the Ansys Composite PrepPost (ACP) package. Deflections and surface strains were measured for the test articles using digital image correlation (DIC), distributed optical fibre sensor (DOFS) and electro resistive strain gauges, which were compared with the finite element analysis (FEA) estimates. Numerical interaction diagrams for the tubes were developed based on maximum stress criteria in the laminate to demonstrate the effect of fibre orientations on the ply-wise failure initiation under axial-torsion loading combinations.

Concrete is a composite material in which cement paste acts as a binding medium for sands and aggregates. The physical and chemical processes that occurs within these constituents of concrete at early stages after mixing, in long-term period or even under exposure to high temperature, are significantly different. Several numerical studies have demonstrated that a homogeneous, isotropic assumption for concrete fails to realistically capture the behavior of large-scale concrete structures. Hence, in this study, different approaches that were developed to model concrete at meso-scale is discussed. In addition to that, different processes which occurs within concrete constituents that need to be considered at meso-scale, are also presented. Thereafter, numerical studies are conducted to illustrate the applicability and robustness of such approaches. Such a numerical meso-scale based approach would also give the designer that flexibility to achieve a targeted concrete performance by altering the constituents’ properties.

Building construction with masonry is a widely practiced form of construction across the world. Masonry members, in general, have poor flexural strength, which needs to be enhanced using materials with high tensile properties, such as steel reinforcement in brick masonry slabs and fabric-reinforced cementitious matrix (FRCM) or engineered cementitious composites (ECC) for wall panels. The existing reinforced brick masonry (RBM) slabs can be strengthened with concrete jacketing with the option of reinforcing bars. The out-of-plane response of the unreinforced masonry (URM) walls, either as load-bearing or infills in moment frames, is especially critical when they get damaged under in-plane shear loads endangering their stability, as evident in past earthquakes. The out-of-plane strength of the masonry walls, either load-bearing or infill walls, can be enhanced by using FRCM or ECC. This paper summarizes the experimental studies on the effectiveness of the strengthening technique for improving the flexural strength of the masonry walls and slabs using concrete jacketing, FRCM, and ECC. The Flexural strength of the URM can be improved up to 4 times by using ECC as retrofitting material. A low-cost ECC was developed at IIT Kanpur, which exhibited a tensile strength of 3 MPa and tensile strain capacity of 1.2%.

The stability behavior of lightweight structural panels, made of laminated composite materials is presented here. The article starts with the introduction of various stability concerns in thin walled structural members, followed by an overview of the “analytical aspects”, “finite element techniques” and the “relevant solution strategies” to investigate the buckling phenomenon of uniformly stressed isotropic plates under in-plane compressive or shear loads. Thereafter, the stability characteristics of laminated composite panels are discussed to highlight the effects of its material coupling (e.g., extension-bending coupling, coupling between the in-plane and shear strains). The representative numerical results are presented on the static and dynamic stability behaviors of constant stiffness composite laminates (CSCL) and variable stiffness composite laminates (VSCL) under various static and dynamic loads.

This study has focused on the instability behavior of the laminated functionally graded CNT reinforced (FG-CNTRC) plate under different types of the non-uniform dynamic in-plane loads. The application of the different non-uniform loads would resemble with the actual operation of the structures. The kinematics of the FG-CNTRC has been modelled based on the Reddy’s third order shear deformation theory. The developed in-plane stresses may not be uniform when the structure is subjected to the non-uniform harmonic edge loads. Hence, the evaluation of the in-plane stresses become necessary prior to the calculation of the critical buckling load of the FG-CNTRC plate. These in-plane stresses have been calculated using the stress recovery procedure implemented in finite element method. Once the critical buckling load of the structure determined, the differential equation of motion of the plate converted into Mathieu type differential equation and solved as the general eigenvalue problem as suggested by Bolotin. The efficacy and flexibility of the present formulation has been validated with the available solution for different geometric parameter of the FG-CNTRC plate. Further, various parametric studies on dynamic instability behavior of the FG-CNTRC plate have presented by considering different parameters like span-thickness ratio, CNT gradation through thickness, aspect ratio, edge constraint, different type of edge load etc.

Modular construction is a relatively innovative construction technique where a building is predominantly made up of a series of prebuilt units, called ‘modules’, which are manufactured in a factory, transported to the site and then joined together to create a larger building. The big advantage to this method of construction is that most of the module interiors/services can be installed in the factory, meaning that on-site construction time is significantly shorter than for conventional construction. Recent numerical studies have developed methods which predict the vibrational response of prefabricated modular tall buildings subjected to the wind loads in its early stages of the design and to provide solutions for controlling the vibrations. A building located in London has been modelled in AXIS VM X4 software and MATLAB code is developed for calculating accelerations of the building through Multi-Modal Analysis and comparing them with the comfort requirements provided by ISO 10137:2007 where peak acceleration limits for tall buildings are provided. Sensitivity analysis has been performed to investigate the impact of various parameters on the peak acceleration of the building.

A new control algorithm called Velocity tracking control (VTC) has been developed for semi active and hybrid control of RC building frame using magneto-rheological (MR) dampers. In VTC, input voltage to MR damper at each time step is directly obtained by using the feedback information available at the previous time step. The efficiency of the control algorithm is compared with that of a few standard control algorithms for both semi active and hybrid control. Conclusions of the study show that the VTC algorithm provides the maximum percentage reduction in the peak inter-story drift among other control algorithms. Further, the percentage reduction of responses per unit control force, is also found to be more for VTC algorithm as compared to other algorithms.

In this chapter structural performance of geo-polymer Concrete Filled UPVC Tubes (GCFUT) subjected to axial compression has been studied. The structural performance has been assessed by investigating confinement and ductility during their axial deformation obtained from load-compression variations. Strain controlled testing was performed to obtain post-peak variation of load-compression curves. UPVC pipes of three diameters 110 mm, 140 mm and 160 mm are filed with two mixes of geo-polymer concrete designed using GGBS. Effect of change in diameter and mix proportion of filled concrete on structural performance of geo-polymer Concrete Filled UPVC Tubes (GCFUT) has been presented. It is found that the UPVC tubes can be employed to offer confinement for enhancing load carrying capacity, energy absorption capacity and ductility in geo-polymer Concrete Filled UPVC Tubes (GCFUT).

Fibre-reinforced polymers or FRPs are durable materials that are highly resistant to corrosive activity, have a high stiffness-to-weight ratio and are ideally suited for the construction of assembly lines into compact modules which can be easily installed. FRP production costs are therefore considerably higher than conventional concrete and steel materials. Hence overall cost savings is either due to decreased weight, faster building speed or lower maintenance and improved life span. In this study, the optimum cross-section of the stiffeners of the deck slab is determined from different shapes and sizes of stiffener, which offers high stiffness and strength. Along with, effect of different longitudinal and transverse modulus of stiffeners on the flexural capacity of deck is determined. It is observed that by keeping longitudinal modulus (E₁) constant while varying the E₁/E₂ ratio, the trapezoidal shape stiffener provides the highest strength and stiffness. On the other hand, keeping E₂ constant and varying the E₁/G₁₂ ratio trapezoidal stiffener shape shows the best result.

This work is focused on the study of postbuckling aspect of laminated composite stiffened plates subjected to parabolic in-plane loading, using finite element method. The eight-noded degenerated shell element and the three-noded degenerated curved beam element with isoparametric formulation with C⁰ continuity (FSDT) of the primary variables are used to model the plate skin and stiffeners, respectively. The postbuckling analysis is carried out by solving the nonlinear load-deformation equation by Crisfield arc-length method. The results obtained from the present formulation are compared with available results to ensure accuracy of the formulation. The linear eigen-value buckling analysis is also performed to compare the results. The Green–Lagrange strain displacement relationship in total Lagrangian coordinate system is adopted in the formulation. The effect of different parameters like lamination scheme, number of layers, aspect ratio, stiffener depth and boundary condition, on the postbuckling response of the plates is considered in the present study.

The present study deals with an open cell shear deformable functionally graded porous beam subjected to in-plane periodic loading to analyze its nonlinear vibration behaviour. The porous beam in this study is modelled based on Timoshenko beam theory i.e., first-order shear deformation theory (FSDT). The porosities are dispersed throughout the thickness of the beam considering uniform and non-uniform symmetric distribution models. For the two distribution systems, the mass density and elasticity moduli of porous beams are considered to vary in the thickness direction. Using Hamilton’s principle, the partial differential equations (PDEs) governing the behaviour of porous beams are derived for the simply supported boundary condition. Then, Galerkin’s method is employed to convert the PDEs to nonlinear ordinary differential equations (ODEs). Further to trace the non-linear vibration behaviour (frequency-amplitude curve) of the porous beam, these ODEs are solved by Incremental Harmonic Balance (IHB) method. A parametric study is presented to assess the influence of porosity, static and dynamic load factors on the vibrational characteristics of the porous beams. As anticipated, the porous beam with non-uniformly symmetric distribution exhibited a higher critical buckling load compared to the uniform distribution of porosity.

With the rapid need for rehabilitation and strengthening of concrete structures, the application of the CFRP (carbon fibre reinforced polymer) is found to be more popular. It is mainly due to their attractive material properties in terms of strength, durability, and minimal influence on the weight of the structure. Also, the ease in the application has attracted the attention of engineers and applicators. In modern construction, only 20–30% of CFRP material properties get utilized in structural strengthening. However, researchers have developed various methods to increase the utilization of the material properties for strengthening concrete and steel structures. One such invention is the application of a prestressed CFRP system. There are various setups developed to prestress CFRP during its application. Prestressing CFRP bands, particularly for axial members, have shown their effectiveness in the strengthening of the member. However, there is still a huge room for research in this technology. The suitability, technical advantage, application methods along with some case studies of this technology are discussed in this chapter. The application of CFRP laminate or sheet as a strengthening method not only contributes to the design optimization but also offers immediate resistance to the existing loads.

A Fiber Reinforced Polymer (FRP)-Concrete composite beam system comprises of several contact interactions, sub-components with varying geometries, and complex material behavior. Evaluating the flexural response of such structures through experimental campaigns is highly expensive and time-consuming as obtaining the desired output variables requires the specimens to be heavily and precisely instrumented. A numerical simulation could provide a much better alternative in this case as it can simulate the complete mechanical response of the physical system with relatively much ease and economy. However, the complexities involved with the problem regarding contact interactions and complex material behavior, make such analysis suffer from several convergence difficulties. The chapter is an attempt to overcome these difficulties by establishing a methodology that can be followed for modeling and analyzing such structures.

Buckling analysis of thick isotropic plates subjected to uniaxial and biaxial in-plane forces is presented using the 5th order shear deformation theory. The 5th order shear deformation theory considers both transverse shear deformation and transverse normal strain deformation effects. The assumed displacement field accounts for non-linear variation of in-plane displacements as well as transverse displacement through the plate thickness. The condition of zero transverse shear stresses on the upper and lower surface of plate is satisfied. Hence, the present formulation does not require any shear correction factor generally associated with the first order shear deformation theory (FSDT). Numerical results for buckling analysis include the effects of side to thickness ratio and plate aspect ratio for simply supported isotropic plates. The results of present theory are compared with classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) and trigonometric shear deformation theory (TSDT).

The present study deals with the numerical investigation of buckling and postbuckling responses and failure of natural fiber-based composites and synthetic fiber-reinforced polymer composites under uni-axial compression. The unidirectional fibers are used for the composite aligned with the (0/90) directions. The plates are modelled using general purpose software Abaqus. All the edges of the plate are simply supported. By implementing the linear buckling analysis, the buckling load has been determined. Using the non-linear analysis and static Riks procedure, the composite's postbuckling behavior has also been predicted. The Tsai hill failure criterion is incorporated in the numerical analysis to predict the first-ply failure in the composite. In this study, three different composite models, i.e., Glass, Carbon and Flax fiber-reinforced composites are considered for the analysis. It is observed that the carbon fiber composite has the better buckling load capacity and the first ply failure load compared to glass and flax fiber-reinforced composites. It is further observed that the flax fiber-reinforced composite performs comparatively similar to the glass fiber reinforced composite. Based on the results, it is expected that the glass fiber reinforced composite can be replaced by the flax fiber-reinforced composites. In this study, the ultimate load has been considered when the plate is unable to take any further load in analysis. To precisely predict the ultimate failure of a composite, a methodology has been proposed to undertake the progressive failure analysis of composite by incorporating the UMAT subroutine in the Abaqus.

The postbuckling response of functionally graded hybrid composite plates with circular cutouts is investigated in this paper. Using the finite element method-based simulation software ABAQUS, a detailed analysis is performed to demonstrate the effect of the location of the circular cutout on the square functionally graded hybrid composite plate. The plate is subjected to uniaxial compressive loading on the plate's edges. Buckling and failure loads for angle-ply layup sequence and quasi-isotropic layup sequence fiber-oriented plates are determined. The Tsai-Hill criterion is used to predict the failure of the first ply on a composite lamina. A comparison is made between all of the composite plates with different sized cutouts. It is concluded that a composite plate with a center cutout provides the most benefits, such as high critical buckling and failure loads in both the layup sequences considered in this study. This is due to the large distance between the cutout location and the loaded edges, as well as the fact that it has minimal effect on the buckling strength of the composite plate.