Proceedings of Italian Concrete Conference 2020/21

The construction sector is the most resource intensive industry in Europe, it uses around 50% of available raw materials and has significant environmental impacts and costs. Construction industry is, therefore, required to become more and more sustainable and the use of Secondary Raw Materials (SRM) represents a viable solution. Research on building materials is, nowadays, working on the valorisation of SRM from different waste streams to replace conventional cements, which production is responsible for energy consumption and CO2 emissions, or aggregates extracted from natural sites. Alkali-activated cements (AACs), among them those based on slags from steel plants (ground-granulated blast-furnace slag - GGBS or GGBFS), activated by alkaline liquids to produce alkali-activated binders (AABs) are considered sustainable alternatives to ordinary Portland cement (OPC). Concretes based on AABs have gained considerable attention due to their reduced environmental impacts and costs combined with high technical performance. This paper reports on promising experimental results achieved for an innovative concrete prepared with an AAB consisting in a combination of GGBS (60% wt), natural calcium carbonate filler (30% wt) and silica fume (10% wt). The concrete has been extensively tested to assess technical properties such as workability and mechanical performance (compressive strength, elastic modulus, stress-strain behaviour). This research encourages the use of AABs in concrete technology and, in general, of recycled materials in the construction sector.

The impact of hurricane Irma devastated coastal areas in South Florida in September 2017. Even though Miami-Dade County did not experience a direct landing, several coastal structures were damaged during the event. Damage was particularly critical for marine docks already deteriorated by corrosion. To address reconstruction needs, the “iDock” was developed as a prototype structure designed to resist severe hurricane loading while guaranteeing superior durability in sub-tropical marine exposure. To achieve the intended targets in terms resilience and durability, the entire structure is reinforced with Fiber Reinforced Polymer (FRP) bars. This paper discusses the design and construction of the dock. The structure is prefabricated to ease operations and achieve accelerated construction. To foster sustainability, the concrete in part of the precast elements is mixed with sea water. Fresh water is increasingly becoming a scarce resource and initiatives to limit its exploitation in the construction industry are gaining momentum.

A 300 km in length railway is under construction in the Jammu-Kashmire region and due to morphology of the area, 90 km of tunnels and several important bridges are required along the line; among them, one will cross the Anji valley at 190 m above the river. It is a cable stayed bridge with a major span of 290 m, a composite steel-concrete truss deck and a 200 m in height single concrete tower the top of which will be at 390 m from the bottom of the valley. The rear stay cables are anchored to both the rear span and to a 43 × 15 × 21 m concrete ballast element. The project will be briefly described including the tests performed in the POLIMI wind tunnel and the construction progress.

The Rose Fitzgerald Kennedy Bridge over the river Barrow is the most iconic element of the N25 - New Ross Bypass project, which is aimed to optimize the traffic across south-eastern Ireland. It extends for almost 900 m, with two 230 m long main spans, and is the world’s longest prestressed concrete extradosed bridge. Several prestressing technologies are installed in the structure, namely bonded post-tensioning tendons and parallel strand stay cables with multi-tubes saddles. After introducing the structural features of an extradosed bridge, the focus is on prestressing systems qualification and installation within the different construction methods adopted.

Sustainability aims to maximize circular economy and durability, by reducing construction costs and maintenance needs and increasing the works lifetime. Brenner Base Tunnel (BBT) Lot Mules 2–3 is conceived, designed, and built with this vision, focusing sustainability and durability as prevalent goals, targeting a 200 years’ lifetime. Specifically, durability is the result of appropriate choices of techniques and materials in planning and design phases, for instance: exposure assessment, attention to construction details and to the use of durable construction materials in relation to the actual attacks. Also, the use of construction, demolition, and excavation waste (CDW) is beneficial, if planned and managed with appropriate characterization systems and production processes.

The Volta School in Basel, designed by the architects Miller & Maranta and the structural engineer Jürg Conzett in 2000, is the first built example of RC wall-and-slab spatial system. This system uses the horizontal stiffness of the floor slabs to support the load bearing walls eccentrically, thus allowing, if certain geometrical conditions are fulfilled, to change the position of the walls floor by floor. In this way the requirements of structural continuity is avoided, in favour of higher architectural freedom. The system presents some challenges in the construction phase and requires close collaboration between the architects and the engineers. This is the reason why there are very few buildings that use this structural system. One of the most recent examples of its application, designed by one of the authors, is the retirement home in Giornico. The design was performed using strut-and-tie and stress fields models, and it is presented in detail in this paper.

The study analyses the different safety formats for non-linear finite element analyses to assess the design strength of reinforced concrete members. In detail, non-linear finite element analyses are developed to reproduce various experimental tests in compliance with the different safety formats analysing the results in terms of resistance and failure mode. Then, some proposals are discussed. Specifically, two preliminary non-linear finite element analyses are suggested to verify which safety format can be used. In addition, in order to always apply all the safety formats for their reduced computational effort, an additional failure mode-based safety factor is presented to assess the design global resistance of reinforced concrete structures.

This work describes the resistance model uncertainties in non-linear finite element analyses for reinforced concrete members under cyclic loads for seismic analyses. In detail, several plane stress finite elements analyses using different numerical codes and considering the possible modelling hypotheses are carried out to reproduce the seismic behaviour of various walls experimentally tested. The global resistances achieved from the numerical analyses are compared to the experimental outcomes to assess the influence of the model uncertainties.

The high mechanical performances showed by geopolymer concrete led several researchers to investigate about possibilities of using this material in reinforced structural elements. Since geopolymer binder has a different microstructure from ordinary Portland Cement (OPC) it is necessary to understand the bonding behavior between geopolymer concrete and steel bar. Generally, it has been observed that geopolymer concrete (GPC) has higher bond strength than OPC due to the higher compression strength and the dense and compact microstructure of GPC. In this context, several authors worked also on bond strength of GPC with glass fiber-reinforced polymer (GFRP) rebars. In this paper the bond-slip behavior of GPC with both steel and GFRP reinforcement bar will be investigated. The results obtained in this work showed that GPC has a higher bond strength than the values purposed by Model Code 2010 for an OPC concrete with the same compression strength. Moreover, sand-coated GFRP bar showed a lower bonding capacity to that of deformed steel bars conventionally used for structural applications.

The confinement with fibre-reinforced polymer (FRP) is one of the most used techniques to enhance strength and ductility of existing reinforced concrete (RC) columns. Although the effective of FRP confining systems on columns with circular, square or rectangular cross sections has been extensively studied and standardized, these results are limited to sections with an aspect ratio between the two sides less than two. However, many applications of wall-like columns (member with rectangular cross section with higher aspect ratios) strengthened with FRP are developed in the practice. Moreover, the prediction of their load carrying capacity still remains of uncertain solution. In order to clarify this issue, a review of the existing analytical models is first presented. Then, available experimental results are selected from the literature to compare the performance of these models. Finally, the results are discussed to quantify their accuracy in the prediction of the axial member capacity.

This study focuses on the development of Glass Fiber Reinforced Polymer (GFRP) reinforcement made with thermoplastic (TP) resin to be deployed in Reinforced Concrete (RC) and Prestressed Concrete (PC) members. GFRP bars made with thermosetting resin are an effective corrosion-resistant solution with positive implications on the durability and sustainability of RC structures. However, the use of thermosetting resin makes manufacturing of complex shapes difficult, generates an inevitable amount of waste during the production process, and prevents recycling the material at the end of its life cycle. The use of TP resin may have a disruptive impact on the industry. It may ease manufacturing, allow the creation of twisted strands for prestressing applications, and promote a steel-like logistic chain that separates the roles of manufacturer and constructor. This paper explores the challenges related to the development of TP-GFRP reinforcement in the form of a 5-mm wire, a 15.2-mm twisted strand, and a 12-mm reinforcing bar.

Recycled aggregates are increasingly being used in the construction industry. Among others, Electric Arc Furnace (EAF) slag aggregates have been proven to be promising both in terms of sustainability and material properties. However, EAF concrete is also characterized by a higher specific weight with respect to natural aggregates (NA) ones and while good results have been obtained for elements subjected to static loads the behavior of EAF RC structures under dynamic loads is yet to be investigated. Therefore, the present paper aims to investigate the seismic response of reinforced concrete (RC) frames made with EAF in comparison to the same frames made with NA concrete.

The uncertainty in the concrete compressive strength is one of the most challenging issues in the seismic assessment of an existing RC building. This works characterizes the compressive concrete strength based on both in-situ destructive and non-destructive tests. A large set of data including (destructive) core tests and SONREB (rebound number S and ultrasonic velocity V) non-destructive test results, measured on the same structural elements of different existing RC buildings, has been collected. Then, a regression model is employed in order to derive predictive expressions for calculating the compressive concrete strength Rc based on the ultrasonic velocity V and on the rebound number S measurements. The work shows also that linear logarithmic regression (V-Rc) can be used instead of the multilinear logarithmic regression (V-S-Rc) without significant loss of accuracy.

In this paper, the assessment of the shear strengthening of a series of RC coupling beams, manufactured in scale 1:2 with a span-to-depth ratio equal to 1.5, is presented. The retrofitting strategy employed to restore or upgrade the load carrying capacity of the structural elements consists in the application of Fabric-Reinforced Cementitious Matrix composite materials. The experimental campaign comprises monotonic and cyclic tests, in order to assess the potentiality of the FRCM overlay under different loading conditions. The efficiency of the retrofitting system is validated by testing non-damaged coupling beams, exploring also the effect of the addition of short PVA fibres to the mixture.

This paper aims at presenting a new model of cladding panels of single-story RC precast buildings. Recent post-earthquake surveys show the high vulnerability of cladding panel-to-structure connections, which failure caused large economic and human losses. Two different three-dimensional nonlinear models are defined: i. a bare model, where the panels are only modeled in terms of mass applied in the floor center of mass; ii. Panels are modelled in terms of mass and stiffness and panel-to-structure connection behavior is taken into account. Panel-to-structure connections are modelled according to recent experimental force-displacement curves. The progressive collapse of the panels during the earthquake is also simulated. A comparison between the bare model and the model with panel is finally carried out.

Recent and past seismic events have emphasized the key role of beam-column joints on the vulnerability of existing RC frame buildings. Indeed, damages and unexpected failure modes of these structural components in some cases resulted the main responsible of a poor seismic response of buildings. The lack of care by past standard codes for the design of beam-column joints and, moreover, the difficulties in modelling and simulating their complex behavior, are clearly highlighted by the available studies of literature, where the attention is mainly focused on the derivation of constitutive laws and numerical modelling approaches. The present paper concerns the numerical study of exterior RC beam–column joints. In particular, starting from the models available in literature, laws able to reproduce the monotonic and cyclic behavior are derived, implemented by using the simple scissors model and subsequently assessed toward experimental tests.

In the last two decades many scientific works on the seismic evaluation procedures for buildings, using nonlinear static analysis (pushover), have been published. Differently there is no much effort available in literature for seismic evaluation of existing bridges, although bridges are strategic infrastructures for every country, with pushover. The aim of the present work is to asses a procedure for existing bridges, using a nonlinear static analysis; the study extends a method proposed for buildings by the same authors (Bergami et al. 2017), the incremental modal pushover analysis (IMPA), that contemplates the two following important aspects that are relevant in the field of seismic analysis of bridges: the intensity of the demand and structural response are correlated; bridges are frequently higher modes sensitive. For all these reasons IMPA for bridges appears as a promising procedure. In this paper the procedure, together with some results of the application on two case study, are presented and discussed.

The beam-column joints are crucial elements where the stresses arriving from the horizontal and vertical structural elements at the boundaries come with very high gradients. These elements are therefore directly involved in the seismic forces transfer. It is well known from recent history that past earthquakes have highlighted a poor performance of the beam-column joints, mainly because, until a few years ago, the joints were not designed, but simply assumed as rigid elements, showing serious limits to seismic actions. The model is based on post-cracking equilibria and it allows to trace the performance of the nodes highlighting the activation thresholds of different failure modes. The model has been validated through a database of 270 experimental tests on beam-column joints, showing, on average, better performance than currently available formulations.

In this work, the performance of concrete tunnel linings subjected to high temperatures is assessed by performing 3D FE simulations. The analyses account for all the different stages of lining construction and use, from its installation, to its service life, to the possible spreading of fire. In order to realistically represent the soil excavation phase and the subsequent lining installation, a step-by-step procedure is followed, whereas a sequentially coupled thermo-mechanical procedure is applied for the fire stage. The behavior of concrete subjected to high temperatures is described by using the non-linear constitutive model “2D-PARC FIRE”. This model considers all the main features governing concrete behavior (i.e. cracking, crushing, shrinkage, creep and time-dependency of concrete mechanical properties) by also including the effects of thermal strains and the degradation of material properties due to fire.

Under seismic load, Reinforced Concrete (RC) members may exhibit a flexure-controlled ductile (F) failure; otherwise, they may exhibit a shear-controlled brittle (S) failure or a combined flexural-shear (FS) failure. The identification of the failure mode determines RC members’ expected (and modelled) strength and deformation capacity. Approaches for the classification of the expected failure modes are proposed in the literature and, in some cases, adopted in codes. However, the use of a “discrete” pre-modelling classification (F/FS/S) does not allow the definition of a unique, failure mode-independent, “modelling structure” valid for whichever structural member. A preliminary study for the evaluation, based on experimental data, of a non-discrete failure mode classification, by means of a “membership function”, is presented. The proposed membership function can be used to preliminary define a unique set of predictive equation for the assessment of the deformation capacity of RC members up to the complete loss of strength resistance.

Construction systems based on cast-in-situ reinforced concrete sandwich (cRCSP) walls represent a very widespread solution for buildings, largely adopted also in earthquake-prone areas. Therefore, seismic performances assessment of such structural systems can be considered critical. This paper aims to contribute to the investigation about seismic behaviour of cast-in-situ reinforced concrete sandwich walls, first of all, starting from a detailed review of both the few experimental and analytical studies available in literature. The experimental results from literature have been collected in a proper reference database and the main existing shear-strength relationships, from codes and literature, have been implemented in order to compare their prediction with the experimental results. Finally, a technical guideline of the Italian Superior Council of Public Works has been considered for the evaluation of the behaviour factor of structural systems with cRCSP walls. The reasonable conservativeness of the so-estimated behaviour factor is confirmed by the analysis of the collected experimental results on the cRCSP walls, which can be extended to the global structural ductility if a sufficient regularity in-plain and in-elevation is provided. Further improvements could be obtained by proper product-testing.

Durability of externally bonded Fibre Reinforced Polymer (FRP) systems is a key concern in the field of civil engineering, due to the actions and harsh conditions these strengthening systems are exposed to during their service life. The paper will present the results of an experimental investigation of the long-term behaviour of the Steel Reinforced Polymer (SRP) system bonded to concrete when subjected to sustained loading. Long-term tests in single-lap shear configuration were performed on specimens constituted by concrete blocks reinforced with two different types of steel fabrics embedded in an epoxy resin. An innovative test setup has been designed with the aim of applying a sustained load for up to six months simultaneously to a considerable amount of specimens under fixed ageing conditions. Results in terms of retained bond strength will be also presented, showing the influence of the long-term loading on the effectiveness of the studied strengthening systems.

This research aims to investigate the potential benefits of using Glass Fiber Reinforced Polymer (GFRP) bars as reinforcement for prestressing applications. Six full-scale specimens 6.1 m long having a 762 × 254 mm cross section with different reinforcement ratios were built and tested. GFRP bars and stirrups were used in place of conventional steel reinforcement. All specimens were tested under four-point bending. The load-deflection response along with the failure modes were evaluated and presented. The test results showed how the different reinforcement ratios affected the behavior of the beams under service and ultimate conditions. A comparison between the experimental results and the analytical predictions from the flexure theory of reinforced concrete was performed. The analysis showed good agreement which explains the consistency of the experimental outcomes. The results of this study provide a strong scientific milestone for optimizing the design of pre-tensioned beams using GFRP reinforcement.

The high vulnerability of prestressed reinforced concrete (PRC) structures to the corrosion degradation has been highlighted by several damage cases occurred in European countries. Therefore, many researchers addressed this important topic in the last decade, carrying out bending test of full-scale PRC beams, to evaluate the residual structural performance of the corroded member.To better understand the global behavior of corroded PRC beams in flexure, the knowledge of fundamental issues such as mechanical properties and bond performance of corroded strands, prestressing action losses, and transmission length variations, is required. At the material scale, some experimental results obtained by direct tension test are available, while the studies on the strand-to-concrete interaction after the corrosion degradation are really few. In this paper, the preliminary results of an experimental campaign aimed to investigate the bond-slip relationship between concrete and artificially corroded strands are presented.

A modification of the variable strut inclination method of the Eurocode 2 (EC2) for the shear strength calculation of reinforced concrete (RC) beams with stirrups is presented. This model incorporates two (rather than one) variable-inclination compression struts. The upper compression strut may have lower inclination than the lower compression strut, which is indicated by the trend of the principal compressive stress direction. Following the theoretical framework of the EC2 approach, the two inclination angles are determined through the lower-bound theorem of plasticity, by solving an optimization problem. The proposed truss model leads to compact closed-form expressions that can be expediently used for practical design purposes. Based on comparison with experimental results, the proposed model proves to be more accurate than the Eurocode approach to predict the actual shear strength of RC beams with stirrups, especially in the range of low amounts of transverse reinforcement where the EC2 model turns out to be very conservative.

The heat generated by the cement hydration reaction increases temperature within concrete elements during the setting and hardening phases, while it starts to develop its physical and mechanical properties. The generated heat, which depends on the physical-chemical properties of the mixture, the geometry of the elements and the boundary conditions, can lead to cracking phenomena that compromise the long-term durability of concrete structures, especially in the case of massive structures. The proposed study presents a numerical procedure aimed at controlling and assessing the time-evolution of the mechanical properties of the mixture, based on experimental temperature measurements performed on samples cast in semi-adiabatic conditions. Considering the variation of several factors (binders, water-cement ratio, element size and formwork), the reported parametric analysis leads to propose simplified design abaci for mitigating the cracking phenomena.

In recent decades, the advancements of building codes favoured the spread of fibre-reinforced concrete (FRC) in common design practice. The unified rules for the material classification and the simplified constitutive laws introduced by the CNR-DT 204 and the fib Model Code 2010, in fact, allow to effectively evaluate the ultimate capacity of FRC members, ensuring adequate safety levels. With reference to the crack openings typical of serviceability limit states, however, the predictions based upon the available simplified approaches are often characterized by a worse approximation. In this paper, starting from the experimental flexural behaviour, we propose alternative procedures for the back-calculation of the uniaxial tensile behaviour of FRC, built on the enforcement of sectional equilibrium at crack openings ranging between 0 and 0.5 mm. The experimental responses of 12 notched beams are finally compared with simplified plane-section analyses and numerical simulations based on non-linear material models available in commercial software.

EN 1994 currently sets classification rules for ordinary composite beams, while slim floor (SF) beams are neglected. SF-beams are integrated into the slab forming a composite element and the effective cross-section for each design situation must be identified in order to determine the calculation procedure for the resistance of the element. Moreover, the bending behaviour of flexural members is highly dependent on their ductility capacity. Many codes such as EN 1998 and EN 1991-1-7 assume that adequate ductility is available. However, securing that the desired ductility is achieved is not a simple task. In addition, the shear connection plays an important role when considering ductility requirements. This paper presents the results of an experimental program aimed to investigate the bending performance of SF-beams by comparing different configurations, while the importance of appropriate detailing is critically revealed by the results. FE analyses are also carried out and validated by test results.

High performance fibre reinforced concrete (HPFRC) is a composite material characterized by improved toughness due to the presence of fibres bridging the cracks. At the present stage of evolution, several codes and design guidelines are available for the application of such material in the construction field. As a consequence, special attention has been paid on the creation of a single reference for the identification, qualification, technical evaluation certification and acceptance control criteria of the FRC commercially available. This paper presents the results collected during a campaign for the initial qualification of a HPFRC mixture. The tests are aimed at certifying the product performance following the indications reported on the recently emitted Italian guidelines. Besides the mandatory initial type test (ITT) further optional tests are performed, e.g. against freezing and thawing actions. Eventually, the collected data are used to define the material constitutive model used to design FRC elements, based on the indications reported on widespread accepted codes.

Calcium SulfoAluminate (CSA) cement is an innovative binder considered a promising alternative to Portland cement thanks to its rapid strength development, good dimensional stability, and high chemical resistance. Moreover, the production of CSA clinker results in less CO2 emissions compared to Portland clinker since it requires a lower burning temperature and less limestone in the raw meal. Ternary binders made by blending Portland cement, CSA clinker, and anhydrite have been developed and used to achieve a wide range of engineering features including early strength development, good workability, and high dimensional stability. However, limited data are available on the structural behavior of concretes mixed with these innovative binders. To address this gap, a laboratory investigation was performed using traditional Portland-based concretes as baseline for comparison. The evolution over time of compressive strength and modulus of elasticity were investigated to evaluate the effect of the binder type. The experimental results were compared to the analytical models of Eurocode 2, Model Code 2010, ACI 318, and ACI 363.

Concrete is the construction material most widely used in the world and the huge volumes produced every year have a high impact on the environment. In this context, there is a growing interest in developing green cementitious materials able to address the ecological issues. This work focuses on the feasibility of using biochar, the solid by-product resulting from biomass pyrolysis, as carbon sequestrating additive in cementitious materials, with the aim of not diminishing their structural performance but even obtaining enhanced mechanical properties. Since biochar is mainly composed by carbon, it is able to capture and store carbon in buildings - in a stable form - for decades. Furthermore, biochar is usually disposed of as waste; thus, its employment in the building industry would promote waste reutilization, by increasing the recycling rate. In order to assess the structural efficiency of biochar-added cementitious materials, their mechanical properties are here properly investigated.

The present research work focuses on the study and design of innovative mix designs of high-performance mortars with biochar, which is a waste material that gives the mortar a green connotation. Dimensional stability of the mortar at the fresh state is assessed through an extrusion test to evaluate the suitability of the material to be produced via 3D printing technology. In addition to the mechanical properties (flexural and compressive strength), the fracture behaviour of the mortar in crack mouth opening displacement mode is investigated. In this experimental campaign, different parameters are studied and their effect on the mechanical performance and fracture behaviour of the innovative green high-performance mortar are investigated, including aggregate/cement ratio, maximum diameter of the aggregate, and type of aggregate.

A design-oriented analytical model able to evaluate the shear capacity of RC beams strengthened with FRP/FRCM sheets or strips oriented in any direction is proposed. The formulation of the model is based on the variable-inclination stress-field approach, aiming to extend the Eurocode 2 framework to beams strengthened in shear using FRP/FRCM. Complete, U-shaped and two-side wrapping schemes are considered. The influences of both steel and fiber composite transverse reinforcements on the orientation of the compressive concrete stress field in the web are taken into account. Interaction between steel and fiber transversal reinforcement is considered, adopting equations able to limit their global efficiencies. Effectiveness of the proposed model adopting different relations for the assessment of the effective composite and steel strains provided by international codes is investigated. Shear capacity values predicted by the model and those obtained using international codes are compared against experimental results proving the efficiency of the proposed model.

The recent earthquake of Amatrice in 2016 had a huge impact on both historical and recent buildings, underlining the needs of strengthening interventions against cyclic actions. Not just masonry buildings suffered the earthquake intensity but even precast industrial buildings showed local damages or even structural failure. For this type of constructions, a possible strengthening intervention is represented by the installation of anti-seismic connection devices. Depending on the connected elements and the device features, several improvements can be obtained. For instance, one of the issues in precast industrial buildings is represented by the cladding system, which is typically made by reinforced concrete panels with significant dimensions. In this paper, an experimental campaign on the cyclic response of a precast beam-panel joint device is proposed, evidencing its performance in cyclic tests and its capability in uncoupling the in-plane cladding system motion compared to the structural motion.

Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) is characterized by high compressive strength, strain-hardening behaviour in tension and very low porosity. After cracking, crack opening is controlled by the fibres. Therefore, UHPFRC is generally considered as a very durable material and is frequently used in combination with reinforcement for elements exposed to severe environmental conditions. However, scientific evidence on the long-term behaviour of reinforcement embedded in UHPFRC is limited, especially if the simultaneous presence of cracks and chemical attack is considered. This contribution presents the results of a preliminary study carried out to characterize the corrosion behaviour of reinforcement in UHPFRC. Mechanical and durability-related properties of a commercial UHPFRC were determined. Accelerated and long-term corrosion tests were initiated on cracked and uncracked prisms reinforced with carbon or stainless steel rebars.

Aggressive environmental conditions can lead to fast deterioration of structures, especially bridges which are highly exposed to severe conditions. Reinforcement corrosion induced by carbonatation or chlorides can cause a constant loss in the structure capacity in time. When severe environmental conditions fall in highly seismic zones the issue gets more complicated and the overall risk increases. Among available retrofitting techniques, composite materials can be used to strengthen and prevent further deterioration. The present paper investigates the effectiveness of FRCM confinement techniques for retrofitting an existing two-span, simply supported reinforced concrete bridge subjected to chloride-induced corrosion. A seismic reliability approach is used for the seismic assessment of the structure. Time-variant reliability profiles are computed for different deterioration and retrofitting scenarios and reliability gains and losses at different time instants and for different retrofitting scenarios can be determined to support decision-making in bridge management policies.

Concrete is well known to be a heterogeneous material that is usually considered homogeneous only referring to a scale of several centimetres. This characteristic makes measuring stresses inside concrete a particularly difficult task. Strains can be measured using several well-known devices. Nevertheless, it is almost impossible to derive a correct estimation of the stress within a concrete structure starting from strain measures, as the modulus of elasticity is variable and unknown and creep strains superimpose elastic ones. A long-term experimental campaign performed to test a stress sensor with the dimensions of a coin to be embedded in concrete is described in the present paper. The effects of creep, shrinkage and external applied load are measured at the scale of the bigger aggregates.

To promote Circular Economy in the construction industry, it is fundamental to reuse waste material as partial replacement of the natural one, reducing the environmental impact of manufacturing processes. The efficient and circular use of materials can be effectively applied to the production of concrete and to the precast industry. To this purpose, Truzzi S.p.A. decided to tackle the problem of the management of residual concrete from the production of precast structural elements. In this framework, a pelletizing agent recently developed by Mapei S.p.A., which transforms the fluid mix into a granular material, has been tested. This paper shows how it can be used in the precast sector. The optimization of the recovery process drove to the generation of “granulato” which is made of natural coarse aggregate covered by a composite layer. “Granulato” has been subsequently used as coarse aggregate, completely substituting the natural one, to produce new concrete. Fresh and hardened concrete properties have been measured and analysed.

In this paper we are reporting the structural response of fourteen concrete plates of 2000 × 2000 × 150 mm of dimensions that were tested in three configurations of load and support positions being reinforced with either reinforcing rebars (RC) or reinforcing rebars together with 35 kg/m3 of steel fibres (R/FRC). Two of the plate have a special reinforcement where the rebars are placed only around the edge of the plates (R/FRC-APC). Two plates are tested for each configuration and with each of the reinforcing solutions. The structural response of the plates is compared in terms of deflection and the opening of cracks among each testing configuration. Provisions of the CNR-DT 204 and EC2-annex L on design of FRC structures are implemented to check the reliability of these approaches. The obtained results highlight the considerable influence of fibers on structural response and cracking behavior of plates and underline the suitability of the material models given in these codes for design and prediction of the load bearing capacity of these elements.

This study presents the results of a wide experimental campaign aimed at characterizing the physical and mechanical response of sustainable cementitious composites produced different types of bio-aggregates (i.e., bamboo particles, wood shavings and rice husk). First of all, based on the specific physical and geometrical properties of the bio-aggregates, an adapted mixing process was performed in order to warranty an adequate moldability. Then, the stress-strain behavior of the hardened samples was investigated up to 28-days by unveiling the influence of the several types of particles on the resulting mechanical response. The results proposed herein demonstrate the high potential of the bio-concretes for being employed as an innovative and sustainable construction materials.

The basis of a possible design and verification approach to the linings of RC tunnels in fire is presented and discussed. Five damage states are identified for the linings, based on the consequences of several real fires occurred in the past. Back analyses are carried out to define the main parameters controlling each damage state, whose temperature range is determined via fluid-dynamic analyses based on fire zone models and Computational Fluid Dynamic Modelling to identify temperature value ranges for the different damage states. Finally, the proposed approach appears to be appropriate for the in-fire analysis of both railway/road tunnels and underground infrastructures for complex researches.

The development of multifunctional cementitious materials is having a great application impact in civil and industrial engineering. The authors have recently developed carbon-added cement-based composites able to integrate both structural and monitoring capabilities. Graphite powder dispersed into the cement matrix in different percentages is under specific investigation in this paper in order to achieve load sensitivity. This filler has been adopted for its scalable application potential, given its relatively low-cost and mixing easiness. Possible applications are in monitoring of infrastructures that require distributed sensing strategies for an effective health assessment during their service life. Note that traditional transducers have several drawbacks due to critical application procedures, durability, maintenance troubles, and high costs, while the proposed composites could be embedded into the road pavement or its substrates and constitute part of the construction itself. This paper presents the results of an experimental campaign of various small- and medium-scale samples and numerical modelling approaches to simulate real applications on roads and bridges. Overall, the paper contributes to demonstrating the effectiveness of these new materials for traffic and weigh-in-motion monitoring.

Existing reinforced concrete buildings in the Mediterranean area are very vulnerable to seismic actions due to lack of proper seismic detailing and poor quality of concrete. Furthermore, they are likely to exhibit significant earthquake damage to non-structural components such as infills and partitions. Reconstruction processes followed to recent seismic events remarked that the repair of non-structural components represents the majority of the repair costs. This makes the study of the seismic response of hollow clay brick infills and their interaction with the surrounding RC frame of paramount importance. Although number of analytical and experimental studies are available on this topic, experimental tests on full scale multistorey RC frame are still lacking. This paper presents the novel experimental facility for pseudo-dynamic tests available the University of Napoli Federico II and the preliminary results on a full-scale two storey infilled RC frame. An-in depth discussion on the design of the experimental test, the input selection and the sub-structuring is reported together with the experimental response and the validation of the testing procedure.

Friction Damper Devices (FDDs) at the Beam-to-Column Connections (BCCs) are a suitable solution to prevent losses of performance due to cracking and bond losses caused by the high percentage of reinforcement that characterize the panel zone of Moment Resistant Frames with Hybrid Steel Trussed-Concrete Beams (HSTCBs). Here it will be shown that excellent seismic performance can be obtained only when FDDs at the BCCs are used in conjunction with self-centering dissipative connections at the column bases. To this aim, comparison of the seismic performance of traditional and innovative RC structures built using HSTCBs is performed, focusing on the different level of damage experienced by RC beams, columns and panel node zones belonging to traditional and innovative frames.

Recent seismic events occurred in Central Italy drew the attention towards the resilience of the Italian road network, which is characterised by a significant number of old reinforced concrete bridges and viaducts. In this context, the fragility assessment of existing bridges is crucial, since their collapse or loss in functionality after earthquakes may lead to significant economic and social consequences. As a part of a more general study oriented to characterize the fragility level of the Central Italy bridge stock, this work focuses on the real case study of the Chiaravalle viaduct, which may be representative of a widespread class of reinforced concrete bridges in Italy: the viaduct is a continuous multi-span bridge consisting of precast simply supported V-shaped beams connected by a continuous slab. A numerical model is developed in order to capture the failure mechanisms most likely to occur for this bridge typology subjected to seismic actions. A probabilistic assessment of the seismic response of the bridge is carried out by performing multiple stripe analysis, considering a seismic scenario consistent with the Chiaravalle site. Fragility curves, built by accounting for the main demand parameters and the relative limit states, provide useful insights about structural deficiencies of the system at hand.

The use of post-installed reinforcing bars to connect existing concrete elements to newly cast concrete has increased significantly in the last decade. Very common applications are connections between reinforced concrete beams/slabs and columns/walls or reinforced concrete columns/walls and foundations. The design of such connections is clearly limited by the need to use straight reinforcing bars. Consequently, a clear understanding of the unique load-displacement properties of the post-installed reinforcing bars, the necessary loading and installation conditions, and the stresses introduced in the concrete members is required. In this paper design methods based on Eurocode 2 and a new approach considering the actual bond-splitting performance of the adhesive are compared and applied to some case studies where post-installed reinforcing bar systems are used for moment resisting connections. Through the design of typical connections, the challenges and the opportunities associated with the use of post-installed reinforcing bars and their proper design are explored.

A large number of research studies have been devoted to the modelling and analysis of infilled Reinforced Concrete (RC) framed buildings under seismic actions; it is well known that infills play a significant role in the overall structural performance. The present work reports the results of the nonlinear static assessment performed on a masonry infilled RC frame building retrofitted with dissipative braces, located in the area struck by the 2016 Central Italy seismic sequence. The building is an interesting case study because it is equipped with dissipative braces and with a monitoring system; the monitoring system recorded the building response to the seismic sequence and consequently the evolution of the structural response with the progressive deterioration of the infill. Numerical analyses were performed by using nonlinear 3D models, considering both the bare and the infilled frame, in order to appraise the interaction of the infills with the RC elements and the dissipative contribution offered by the dissipative bracing system; an alternative retrofitting approach, finalized to prevent non-structural damage, according to the Bergami-Nuti procedure is finally proposed.

The analysis of reinforced concrete (RC) infrastructure in aggressive environments is a rather challenging task. Nonetheless, it is essential to design new structures as well as to predict the residual life of existing constructions and to plan suitable maintenance interventions. Therefore, this work illustrates the preliminary version of a comprehensive numerical framework conceived to assess the evolution in time of the capacity of RC structures exposed to chlorides, with focus on bridges. A nonlinear dynamic model is first developed by means of the finite element method in the attempt to simulate the transport of chlorides, taking into account binding capacity of concrete as well as the effects due to temperature and moisture. This model is then employed to estimate the free chloride content during the lifetime. Such a result is finally used to evaluate the corrosion current density and the pitting corrosion of the reinforcing bars in order to estimate the pier capacity.

In this paper, the results of the performance-based earthquake engineering (PBEE) analysis, carried out to assess the seismic behaviour of short-medium span steel-concrete composite I-girder bridges, are presented and discussed. The selected case study is part of a group of bridges analysed within the SEQBRI project, funded in 2012 by the European Union, which deals with a systematic development of the PBEE analysis for short-medium span steel-concrete composite I-girder bridges. In this respect, fragility and damage analysis of the selected bridge are performed using a proper component-based numerical model along with wide experimental campaign. These outcomes are then integrated in the decision-making analysis, where the selected decision variable is the repair cost ratio of the bridge. The results show the good performances of short medium span steel-concrete composite bridges, both for minor and major damage scenarios.

This paper aims to present the results of a finite element modelling (FEM) study on the flexural behaviour of Reinforced Concrete (RC) columns retrofitted with RC jackets. The RC jacketing technique is widely used to improve the structural performance of substandard RC columns. However, the relative slip between the old and new concrete can have a significant impact on the flexibility and strength of the retrofitted column, and limited studies have investigated numerical modeling strategies to address this. The proposed FEM approach uses fiber-section beam elements connected by a non-linear interface, and the results highlight the difference from the usual assumption of monolithic behaviour. The monolithic assumption is a common hypothesis in International Technical codes for RC jacketing design and is affected by empirical factors known as monolithicity factors, which are difficult to assess. The study also presents the development of a software package that performs static non-linear analysis of RC jacketed columns and evaluates the actual monolithicity factor by using the OpenSees finite element framework and Matlab for a user-friendly Graphical User Interface (GUI). The fiber-section approach models the flexural performance of the column, and the bond between the old and new columns is considered through a distribution of non-linear springs.

Worldwide, substandard Reinforced Concrete (RC) buildings with unreinforced beam-column joints are widespread also in seismic prone areas. This work presents the performed experimental campaign related to cyclic tests on exterior unreinforced joints. The main investigated parameters are: the joint aspect ratio, the design typology for the beam-column sub-assembly, the beam longitudinal reinforcement amount, and the longitudinal reinforcement typology. The effect of such parameters on the seismic response is first investigated experimentally. Then a modelling proposal for exterior unreinforced joints is described for exterior unreinforced joints with plain bars. The model is numerically efficient for extensive nonlinear analyses, based on experimental tests, easily implementable in common software platforms, and compatible with whatever modelling strategies adopted for the other RC members. The validation of such model is also performed through numerical-versus-experimental comparisons at the scale of the beam-column sub-assembly and at the scale of a whole frame.

Fib Bulletin 80 proposes two methods for the recalibration of the partial safety factors specific for existing reinforced concrete structures and infrastructures taking into account different issues: the residual service life, information deriving from tests, measurements of variable actions and lower target reliability according to economical and human safety criteria. The methods presented in fib Bulletin 80 have been used to assess an existing prestressed concrete bridge built in the 90s. Successively, the results are compared to the outcomes achieved using the approach of EN1990.

Recycling concrete construction and demolition waste is a promising way towards sustainable construction. Indeed, replacing natural aggregates with recycled concrete aggregates promotes the natural resources conservation and reduces the environmental impact of concrete. This work reports on the mechanical properties of concretes with recycled aggregates obtained from two different parent concretes, belonging to the structure of Cagliari football stadium. The main aim is to verify the possibility of using concrete debris in the new structural concrete as recycled aggregates. The effects of parent concretes on properties of coarse recycled aggregates and of new structural concrete with these aggregates are investigated. Mechanical properties (compressive strength, splitting tensile strength and modulus of elasticity) of recycled concretes have been assessed and analysed. The role of the parent concrete has been discussed and some observations are drawn.

The Eurocode defines several ground types for the seismic structural analysis, but what ground type has to be adopted for the bridge piers in water of the Volta Bridge in Ghana, founded on four/six raked piles embedded in rock and with overlying layers of dense and soft sand? The structure is well anchored in the rock (ground type A), but the presence of top layers of sand puts it in the nominal ground type of class D or other. The analysis has been carried out assuming ground type A, and considering the structural interaction with the sandy soil. Two analysis methods are used, as follows: 1) Pseudo-Static Analysis with the Mononobe-Okabe solution, typically applied for the seismic earth pressures on retaining walls; 2) Dynamic Modal Response Spectrum Analysis, modelling the soil with equivalent mass and stiffness.