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Cranes are employed to lift precast concrete girders during their construction. Presently, there is no recommendation for operational velocities during girder assemblage, particularly for long elements; simultaneously, several accidents have been reported during the transitory phase of girder motion. Since this mechanical problem has been examined in technical literature using a static approach, the present research study aims to investigate the dynamical behavior of a long, prestressed concrete girder by determining critical operational velocities according to crane movements. Prestressing cables' eccentricity and lifting loop position deviation were accounted for in 3D finite element simulations of a 40 m span precast prestressed concrete girder. Transient nonlinear analyses to obtain stresses and deflections were performed, so as to account for the large deformation behavior of the motion. A frequency domain approach was employed to analyze the time history results using the girder's natural frequencies obtained by modal analysis. The finite element model was developed to simulate upward, downward, and lateral girder movements. The most significant displacements and stresses were observed in the highest girder acceleration peaks, amplified by eccentricities. Safety against cracking and subsequent failure during vertical and lateral movements was ensured for crane operating accelerations of 0.02 g (v = 20 cm/s) and 0.007 g (v = 7 cm/s), respectively. Compared with the usual static analysis, for the critical case investigated, the inertial effect intensified the tensile stresses by 27 times, increased the compressive stresses by 11%, and increased the girder deflection by 3 times. [ABSTRACT FROM AUTHOR]

To meet the increasing demands for innovations in precast systems with high seismic resistance, in this study, we introduced a novel seismic upgrading technique for roof beam-column (RBC) connections, termed the targeted seismic upgrading (TSU) method, incorporating the innovative seismic safety key (SSK) devices we developed. These devices significantly enhance seismic resilience, offering a substantial improvement over traditional pin-based RBC connections in precast structures, which are known to have limited effectiveness. Our experimental tests on half-scale models of conventional RBC connections, coupled with comprehensive refined finite element method-based nonlinear analytical studies, conclusively demonstrated the enhanced seismic retrofitting capabilities of RBC connections augmented with SSK devices. The paper delineates a technical procedure for applying the SSK, our proprietary innovation, for the targeted seismic upgrading of RBC connections within modern precast systems. Notably, the SSK-upgraded RBC connections exhibited a marked increase in safety, as evidenced by results from experimentally validated nonlinear three-dimensional micro-analytical models. The incorporated flexible design elements in the TSU method ensure its high effectiveness and general applicability for seismic upgrading of both existing and new precast industrial hall structures, offering a significant advancement in this specific seismic engineering topic [ABSTRACT FROM AUTHOR]

Precast structures are widely used in Southern Europe particularly for industrial buildings. Most of such buildings have been built before the enforcement of modern anti-seismic regulations showing a poor performance during past major earthquakes. Focusing on existing one-storey precast industrial buildings, the paper investigates the influence of modelling choices on the risk assessment, direct losses, and required structure retrofit time. RC forks, cladding panels, and elements connections were specifically considered. A precast industrial building with structural details compatible with 1980s Italian regulations was selected and analysed. In general, the failure was associated with the collapse of roof elements. [ABSTRACT FROM AUTHOR]

In the era of energy conservation and environmental protection, as well as the industrialization of buildings, precast concrete (PC) structures have been developed and increasingly applied in construction industries due to their advantages of outstanding workability and ecofriendliness. In order to verify the reliability of overlapping U-bar loop connections and a modified form of these connections, and study the seismic performance of PC wall–beam–slab joints with these connection methods, three full-scale wall–beam–slab joints were designed and tested under low reversed cyclic loading, including one cast-in-place (CIP) specimen and two PC specimens. Based on the test results, the seismic performance of the PC joints was studied by comparing their damage process, hysteretic loops and skeleton curves, load-carrying capacity, ductility, equivalent stiffness, and energy dissipation with those of the CIP joint. After analyzing the experimental results, the following conclusions can be drawn: the overlapping U-bar loop connection and its modified form are effective and reasonable; the specimen with the modified connection form showed slightly better mechanical properties; the failure mode of the PC joints was consistent with that of the CIP joint; and the generation, distribution, and development of cracks in the PC specimens were similar to those in the CIP specimen. In addition, the stiffness of the PC joints was similar to that of the CIP joint, and the load-carrying capacity, ductility, and energy dissipation of the PC joints were better than those of the CIP joint. Moreover, the research in this paper can also provide some guidance for assembling wall–beam–slab joints in PC shear wall structures. [ABSTRACT FROM AUTHOR]

Dry connections primarily consist of high-strength bolts and steel plates. They are commonly used in precast structures as they maximise time efficiency in the assembly stage compared with conventional methods. In this study, an embedded horizontal dry connection was developed using a square-shaped ring connector, high-strength hex nuts and flat washers, and grout for assembling precast concrete shear walls. Using Abaqus CAE 6.14, a numerical study was conducted on two full-scale RC shear walls including one monolithic and one precast specimen to assess the seismic performance of the bolted connection under the combined effect of axial and fully reversed cyclic loading. The average displacement ductility ratio of the precast specimen integrating the bolted connection was three times as much as the reference specimen. However, its relative energy dissipation capacity and shear strength were 21.94% and 27.92% lower, respectively. A parametric study was also carried out on the thickness and grade of the ring connector, grade of the vertical steel bars, number of ring connectors, and diameter of the vertical steel bars at the connection joints. Results showed that the seismic performance of the bolted connection was highly dependent on the bar diameter and number of ring connectors. [ABSTRACT FROM AUTHOR]

Connections in the assembled precast elements become essential locations for creating structural continuity. However, the construction challenges of conventional steel sleeve connections, such as rebar embedment length, rebar congestion, and formed grout defects (i.e., voids), are still a concern area for researchers and engineers. In this study, a proposed ultrahigh performance concrete (UHPC) grouted sleeve connection was presented for assembled precast elements, which might reduce defects, enhance durability, and accelerate structure construction. The tensile test of grouted sleeve connection with different grouting materials, rebar diameters, and anchoring lengths was conducted to determine an optimal anchoring length used in the flexural design. The precast specimens with the UHPC grouted sleeve connection were tested under flexural load. Also, strain changes in concrete, sleeve, and rebar were reported in tensile and flexural tests. The tensile test results showed two types of failure modes, the rebar rupture and bond failure between rebar and grouting. The recommended rebar anchoring length in the flexural design was six times the rebar diameter. The flexural test results showed that the precast specimen with or without the shear key has a similar failure mode as compared to the cast‐in‐place specimen, while their average cracking load, yield load, and ultimate load were 27.9%, 11.0%, and 7.4%, respectively, which is less than those of the cast‐in‐place specimen. Also, the flexural cracking resistance was the highest in the sleeve segment, followed by the joint region and the rebar segment. This study provides a reference for the design of the UHPC grouted sleeve connection for assembled precast elements. [ABSTRACT FROM AUTHOR]

Typically, the columns of the prefabricated reinforced concrete (RC) industrial buildings and warehouses with large clear storey heights are very slender, with aspect ratios (shear span to width) larger than 10. In addition to supporting the gravity loads, the columns also provide strength, stiffness, dissipation and displacement capacity of the primary lateral-load resisting system. However, current empirical relationships that predict the non-linear response and failure mechanisms of RC columns have been developed mainly for lower aspect ratios (< 7), typical of ordinary multi-storey buildings or short-to-medium bridge piers. What makes slender columns different is their predominant flexural response, larger drifts at nominal strength and corresponding lower ductility demands, smaller ratios between the strain penetration and plastic hinge lengths to the element shear span and risk of P-Delta instability. Therefore, the direct application of analytical models available in the literature to slender columns poses a risk of overestimation of their deformation and dissipative capacity. In turns this could lead to the underestimation of their displacement demand, overall damage and collapse probability of the primary seismic-resisting and load-bearing system. In the present research extensive analysis on the non-linear response of slender columns was performed based on observed post-earthquake damage to buildings in Italy and Turkey, experimental data and numerical predictions of the failure patterns through non-linear fiber element models. The influence of the foundation flexibility and the presence of industrial floor was also investigated. The outcome is a simplified analytical methodology for the prediction of the non-linear force–deformation response and possible failure mechanisms of slender precast columns due to rebar buckling or P-Delta effects, as a fundamental step towards the seismic assessment of the global structural performance and cost-efficient retrofit solutions for precast concrete industrial buildings. [ABSTRACT FROM AUTHOR]

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Disturbance/discomfort caused by vibrations, induced by pedestrian walking on slabs in residential/office buildings, is a typical design issue for lightweight slender slabs, including prestressed concrete ones. Precast slabs are typically made with pretensioned members which allow for only partial collaboration in the transverse slab direction, which becomes even less effective when they are dry‐assembled without cast‐in‐situ topping since it relies on the arrangement of mutual mechanical connections only. This study investigates through tests and numerical analyses the response of slender precast long‐span slabs made with voided members, dry‐assembled with mechanical connections, when subjected to vibrations generated by human activities. A parametric set of dynamic modal and time‐history analyses encompassing floor member geometry, connection arrangement, mass, and damping, is carried out. The numerical models are validated against results from an experimental test program carried out on two decks of a prototype precast building. The tests and the numerical models allowed to characterize the fundamental dynamic properties of the slab and its vibrational performance, identifying the most efficient technological solutions among those investigated to mitigate human‐induced vibrations [ABSTRACT FROM AUTHOR]

This article describes the publicly available dataset of multiple shaking table tests on a restrained rocking and sliding bridge system exhibiting negative lateral stiffness. Given the scarcity of experimental campaigns on such systems, this dataset is valuable for the development and validation of analytical and numerical models, with 184 tests. This large body of data allows the models to be validated in a statistical sense. This work describes in detail the specimen and its construction, as well as all instrumentation used during the tests. It presents the organization of the shared data, and concludes with some examples of how the available data can be postprocessed for assessing the behavior of the system. [ABSTRACT FROM AUTHOR]

Recent earthquakes in southern Europe highlighted that the connections of cladding panels to R.C. frames in precast buildings had a major role in the structural collapse. For this reason, there is an urgent need for a review of the design methods for these connections as well as for an improvement in the manufacturing technology. This article aimed to assess the efficiency of dissipative panel-to-structure and roof connections in R.C. precast buildings. A parametric study consisting of linear and non-linear analyses on one case-study building is performed. Different sensitivity analyses are performed varying their mechanical properties (i.e., stiffness, strength, and ductility) to analyze the behavior of the CP/frame connections. The study focuses on dissipative connections with an elastic–plastic behavior, placed between cladding panels (CPs) and frames in precast buildings with stacked horizontal cladding panels. The introduction of dissipative CP/frame connections implies the inclusion of panels in the global seismic resisting system. The “panels + frame” system highlights a high stiffness until the yield strength of the CP/frame connections is reached. The results, obtained from non-linear dynamic analyses (NLDAs), clearly show how the proposed connection improves the structural seismic performance. By contrast, this is no longer true for R.C. precast structures with flexible diaphragms, especially for intermediate columns, far from panels aligned to seismic action. In this case, significant and unexpected axial forces arise on out-of-plane connections between panels and columns. The integration of an efficient diaphragm is essential to prevent these critical issues both on intermediate columns and CP/column connections; it enables the dissipative capacity of the “panels + frame” system, and it significantly limits the forces and displacements of intermediate alignments. Unfortunately, the achievement of a rigid diaphragm is not always feasible in precast buildings. A possible alternative to activate dissipative capacities of the roof diaphragm with limited in-plane stiffness is the use of dissipative connections linking roof beams and main beams. The solutions described in this article can be applied both in the design of new buildings and for the seismic upgrading of existing ones with easy-to-install and low-impact applications.

The seismic performance of precast portal frames typical of the industrial and commercial sector could be generally improved by providing additional mechanical devices at the beam-to-column joint. Such devices could provide an additional degree of fixity and energy dissipation in a joint generally characterized by a dry hinged connection, adopted to speed-up the construction phase. Another advantage of placing additional devices at the beam-to-column joint is the possibility to act as a fuse, concentrating the seismic damage on few sacrificial and replaceable elements. A procedure to design precast portal frames adopting additional devices is provided herein. The procedure moves from the Displacement-Based Design methodology proposed by M.J.N. Priestley, and it is applicable for both the design of new structures and the retrofit of existing ones. After the derivation of the required analytical formulations, the procedure is applied to select the additional devices for a new and an existing structural system. The validation through non-linear time history analyses allows to highlight the advantages and drawbacks of the considered devices and to prove the effectiveness of the proposed design procedure. [ABSTRACT FROM AUTHOR]

New precast frame industrial structures are seismically designed according to reliable modern criteria. However, most of the existing built stock hosting many workers and both regular and strategic industrial activities was designed and detailed neglecting the earthquake load or according to outdated seismic design criteria and regulations. Its seismic retrofit is a main challenge for the Engineering Community and a critical objective for institutional and private bodies. Among the envisaged solutions, the introduction of dissipative braces appears to be promising, although mostly inapplicable for these buildings, due to the brace lengths required by their typical large dimensions and the related proportioning against buckling. In this paper, an innovative seismic retrofitting technique based on monolateral dissipative bracing is investigated. The device proposed in this paper, yet in phase of preliminary design and testing, dissipates energy through friction in tension only while freely deforming in compression, which makes the issue related to compressive buckling irrelevant. A numerical analysis is carried out to investigate the efficiency of the proposed device in seismic retrofitting of precast industrial frame buildings with the aim to explore its feasibility and to better orient the definition of the slip threshold load range and the future development of the physical device. The simplified Capacity Spectrum Method (CSM) is employed for the global framing of the structural behaviour of the highly nonlinear retrofitted structures under seismic actions. A numerical tool is set to automatically apply the CSM based on the definition of few main parameters governing the seismic response of precast frame structures. The efficacy of the CSM is critically analysed through the comparison with the results of a set of nonlinear dynamic analyses. A smart simplified design process aimed at framing the most efficient threshold slip/yield load of the device given an existing structural configuration is presented with the application of the CSM through the identification of the most efficient performance indicator related to either displacement, shear force, equivalent dissipation of energy or a combination of them. [ABSTRACT FROM AUTHOR]

Shear connections in prefabricated concrete buildings are important for the structural performance in both the serviceability and the ultimate limit state. A normal force has a large impact on the shear strength and deformation capacity, however, no experimental record includes compression–shear and tension–shear interaction. This article presents an experimental investigation of keyed shear connections with looped U‐bars subjected to combinations of shear and normal forces. The tests were performed in a custom‐built double frame, where forces could be applied in two perpendicular directions, which was utilized to introduce normal and shear forces. The load combinations ranged from pure tension, over shear–tension and pure shear to shear–compression. The results include load–displacement relationships supplemented by digital image correlation (DIC) results to exemplify the experimental findings and underline the influence of a normal force on the behavior. It was found that a compressive normal force has a positive influence on the shear capacity in the entire displacement domain tested. A tensile normal force reduces not only the shear capacity but also the deformation capacity of the connection. The ultimate shear load was associated with failure in the joint mortar, which in all cases took place as a local key corner shearing. This article constitutes Part I of the investigation, while Part II introduces rigid‐plastic modeling of the ultimate load carrying capacity. [ABSTRACT FROM AUTHOR]

When the structural capacity of precast concrete structures is to be determined, reliable and practical models for estimation of the ultimate load carrying capacity of the structural connections are essential. In this paper, rigid‐plastic upper bound solutions for the load carrying capacity of keyed shear connections subjected to shear and normal forces are derived and compared to experimental results. The solutions are based on two idealized failure mechanisms involving complete key cut off and local key corner shearing, respectively. The solutions furnish a tool to design connections for the most ductile failure mode, which according to experimental observations is the one with local key corner shearing. Comparison with test results shows that satisfactory overall agreement is found, when appropriate material parameters are adopted. This includes an effectiveness factor, which in this study has been taken from previous studies of similar problems, and an internal angle of friction for mortar in the range of 30°–34°. The agreement is better for combinations of shear and compression, whereas the case of shear combined with large tension forces (i.e., half the yield capacity of the U‐bars) is overestimated by the solutions. Based on the results, it can be recommended that the solutions may be applied in practice using the lower limit for the internal angle of friction, and provided that precaution are taken in cases where the connections are utilized to transfer tension. [ABSTRACT FROM AUTHOR]

Following the empirical observation of widespread collapses of cladding panel connections of precast industrial buildings under recent seismic events, new design solutions have been developed in the framework of the European project SAFECLADDING, including isostatic systems effectively decoupling the seismic response of frame structure and cladding panels. The present paper is aimed at evaluating the seismic response and vulnerability of precast frame structures employing pendulum, cantilever, and rocking cladding connection systems. Within the framework of the research project RINTC–Implicit seismic risk of code-conforming structures funded by the Italian Civil Protection Department within the ReLUIS program, the seismic performance of a typical precast industrial building has been assessed with a probabilistic approach based on the results of static and multi-stripe dynamic non-linear analyses. The seismic vulnerability assessment of each structural system has been carried out with reference to life safety and damage limit states considering three sites of increasing seismic hazard in Italy. The effect of distributed panel mass modeling vs. more common lumped mass modeling has been analyzed and critically commented based on the results of demand over capacity (D/C) ratios. Moreover, biaxial seismic D/C ratios have been evaluated for realistic strong hinge connections for cladding panels.

The main aim of this study was to assess the suitability of different existing test setups for the mechanical characterization of a dimpled interface obtained by casting concrete against dimpled high‐density polyethylene (HDPE) membrane. Even though this type of interface roughening is widely used, especially for monolithic connections between precast elements, to the best of the authors' knowledge there is no research providing any data regarding its roughness parameters, tension, and shear strength, nor its failure modes. To this end, a two‐fold objective was established for this research: (a) to identify and analyze, from a technical standpoint, the available test configurations for characterizing the mechanical performance of interfaces, and (b) to perform an extensive experimental program devoted to characterizing the mechanical performance of a dimpled HDPE membrane—cast concrete interface. The suitability of each test for reproducing the expected stress state and the actual resistance mechanism was analyzed. Moreover, a comparison between tension and shear tests, including its main advantages and disadvantaged are also presented. [ABSTRACT FROM AUTHOR]

The performance of precast concrete structures is greatly influenced by the response of beam–to-column connections. In this study, a new moment resisting precast concrete beam-column connection detail with post-tensioning bolts, made out of high yield strength spring steel, has been experimentally investigated as an alternative to the conventional precast moment resisting connections. Precast specimens and an aseismic monolithic reference specimen have been tested under reverse cycling loads. The contribution of the mild steel in the connection region to the flexural moment capacity, and to the initial pre-stressing force on post-tensioning bolt have been the main test variables. The moment capacity, stiffness, energy dissipation capacity and the residual displacement performance of the precast connections have been compared with those of the aseismically detailed monolithic connection. The conducted tests reveal that the connection detail with steel corbel along with the post-tensioning bolt and mild steel has superior performance properties as compared to the companion precast specimens.

As widely known, connections performance under seismic loads can significantly affect the structural response of RC precast buildings. Within the scientific community, an increasing number of studies has been carried out on this topic, in the light of the recent earthquake aftermaths all over Europe. Indeed, connections turned out to be the weakest part of the precast structures and their failure often provoked the global collapse of the whole building. The present study aims at assessing the seismic behavior of a single-story RC precast building in terms of global collapse implementing two different models of the beam-to-column connection, a simplified and a refined one. A lumped plasticity approach is used to simulate the structural nonlinear behavior at the column base. In order to assess the refined connection model, a preliminary scheme with an isolated single dowel is validated by comparing the pushover outcomes with experimental results from literature. Nonlinear static and dynamic analyses are performed on two models of a 3D single-story RC precast building, one implementing the simple beam-to-column connection model and the other one implementing the refined mode. The comparison clearly shows that the differences are negligible if the global collapse limit state is considered.

The aim of this work is to propose an efficient tool for the design of the monitoring system of precast reinforced concrete industrial buildings in seismic hazard zones, enabling the rapid post-earthquake damage assessment. The methodology, designated as spatio-temporal online monitoring (STOM) is performed by analyzing data obtained from a set of bi-directional accelerometers integrated in smart columns within the building. Acceleration records are converted into inter-story drift ratio (IDR) data, designated as engineering demand parameters, by double integration. Then, calculated IDRs are compared to three levels of alert thresholds meaning that, for the selected damage state, the structure is classified as apparently safe, restricted use or unsafe, corresponding to slight damage, moderate damage and severe damage. Finally, the STOM results trigger visual inspections, thus representing the main inputs needed by engineers in order to evaluate the structural health status and eventually decide for further actions. Measurements data are collected across time as well as space to ensure greater robustness and effectiveness. The STOM methodology allows the preliminary design, i.e., number and location of sensors and optimal demand thresholds, by exploiting the receiver operating characteristics (ROC) analysis, which classifies the different options on the basis of their performance in reporting true damage scenarios with respect to false alarms. Hence, seismic monitoring data are used in conjunction with the pre-evaluated alert states as an engineering decision-support tool for the post-earthquake diagnosis of the structure. [ABSTRACT FROM AUTHOR]

The interaction between cladding panels and the main structure is a crucial point to assess the seismic response, and above all the structural safety, of RC precast industrial building. In the past, connections were often designed to allow construction tolerances and to accommodate both thermal and wind-induced displacements. The lack of specific details to allow relative in-plane displacements between cladding panels and the main structure often led to the participation of cladding panels in the structure seismic-resistant system with consequent connection failures. In the last decades, a lot of experimental tests were performed to investigate the in-plane performance of panel connections, and some design recommendations have been developed accordingly. In the out-of-plane direction, the connections were often considered to be infinitely rigid and not to suffer any damage by the seismic load. This work deals with the out-of-plane response of panel-to-structure connections for vertical panels typical of industrial and commercial precast buildings. Both standard hammer-head strap and new devices, called SismoSafe, were investigated. Tests were performed in the Structures and Materials Testing Laboratory of the Department of Civil and Environmental Engineering of Florence, where a specific setup was designed to perform cyclic and monotonic tests on the connection devices. Standard connections showed a rather limited resistance, while the innovative connections exhibited a high out-of-plane resistance. Numerical analyses were also performed on a case study building to evaluate the distribution of the out-of-plane demand on the connections. [ABSTRACT FROM AUTHOR]

Economic losses associated with the structural and non-structural damage occurring after an earthquake are of particular importance in the case of industrial buildings due to the consequences of such losses on the local economy and employment level. The seismic sequences that hit the industrial area of Emilia-Romagna region of Italy in 2012 represent an emblematic example. In this earthquake event, major damage on poorly performing precast structures was recorded: many buildings were severely damaged and experienced partial or full collapse. The level of the recorded damage was related to a design lacking modern seismic detailing and to a non-up-to-date evaluation of the seismic hazard: in fact, several industrial buildings, typically one storey precast reinforced concrete (RC) structures, were designed to transfer horizontal loads (i.e. between roof elements and supporting beam or main girder and supporting columns) through either friction or under-designed mechanical connections. The aim of this paper is to provide insights on the evaluation of direct losses in the case of precast RC structures typical of the Italian industrial sector, particularly for buildings built before the enforcement of modern seismic codes. A simplified displacement-based seismic loss assessment procedure is proposed and applied to a selected case study and comparisons are made with the results obtained from non-linear time history analyses on simplified (i.e. single column models) and complete three-dimensional models. Retrofit solutions are proposed and their influence on the collapse probability of the structural elements and on the economic losses is evaluated. [ABSTRACT FROM AUTHOR]

• U-bars with a lap length of 15 times the bar diameter achieves the same load-bearing capacity as straight-through bars. • Groove-and-tongue joints have a positive impact on the bending performance of panels. • Established a Strut-and-Tie model for lapped U-bars. • Analyzed the interaction between U-bars and core concrete, and determined the calculation method for their contact height. A comprehensive experimental campaign was carried out to investigate the flexural behavior of wet joints provided with lapped U-bars connecting two precast concrete panels. Eleven assemblies were tested in 4-point bending. Nine assemblies had wet groove-and-tongue joints provided with U-bars, and different values for the overlap length, joint width, and concrete strength. As a reference, the remaining two assemblies had wet groove-and-tongue or flat joints reinforced with straight-through bars. All the assemblies but two were provided with water-stop strips. The test results show that a lap length of 15 times the bar diameter is sufficient to guarantee the same bending capacity as straight-through bars. Based on the deformations of the panels subjected to bending, a strut-and-tie model was developed to predict the flexural capacity of linear wet joints provided with lapped U-bars. The proposed model effectively predicts the flexural capacity of the assembly of two panels since the theoretical predictions and the test results differ by less than 10%. [ABSTRACT FROM AUTHOR]

The seismic performance of precast frame structures strongly depends on the mechanical devices connecting both structural and non-structural elements. Following recent post-earthquake field observations of unintended seismic interaction of the cladding panels with the frame structure, the seismic design of the cladded system is currently being critically examined by the scientific community. Design solutions involving a controlled cladding-structure interaction have been proposed to address this problem. However, the frame-panel interaction may draw high stresses into the roof diaphragm, as a consequence of the stiffening of the external frames only. This paper presents a parametric study based on linear and non-linear dynamic analyses investigating different levels of interaction among frames, panels, and diaphragm system. The results show how the deck and cladding connections influence the seismic behaviour of the structure. Innovative fastening systems aimed at enhancing the seismic performance of the structure are proposed based on the use of dissipative connection devices inserted into both cladding and deck components. [ABSTRACT FROM AUTHOR]

The cladding‐structure interaction of precast concrete frame systems under seismic action has not been properly addressed in the past, as shown by several failures occurred under recent earthquakes in Southern Europe, which point out the need of a revision of the current design practice and technology. Dissipative systems of connections are proposed to this purpose within a general framework for seismic design of precast structures with cladding panels. The proposed connection systems consist of friction‐based or plasticity‐based devices interposed in between adjacent cladding panels or between the panels and the resisting frame to control the level of transferred forces and limit the displacements of the structure. Monotonic and cyclic experimental tests are carried out on both single connection devices and structural sub‐assemblies of two panels. Furthermore, cyclic and pseudo‐dynamic tests on a full‐scale prototype of precast structure with cladding panels are performed. The influence on the structural response of silicone sealant is also investigated through experimental testing. The effectiveness of the tested dissipative connections of the cladding panels in enhancing the seismic performance of precast structures is demonstrated by means of nonlinear dynamic analyses considering the influence of the roof diaphragm action. Design guidelines are finally provided for both single connectors and panel structural assemblies based on equilibrium and capacity design criteria. [ABSTRACT FROM AUTHOR]

Highlights • Two partially precast SRC columns with precast RPC outer-part are presented. • Effects of section shape, stirrup spacing and axial compression were examined. • A model for calculating the seismic bending moment capacity was proposed. Abstract This paper aims to develop two kinds of innovative precast steel reinforced concrete columns, which are partially precast steel reinforced concrete (PPSRC) columns and hollow precast steel reinforced concrete (HPSRC) columns. Both the two kinds of composite columns have precast reactive powder concrete (RPC) shells, and the PPSRC column has a cast-in-place column core. In this paper, a series of cyclic loading tests on 10 column specimens subjected to combined static axial loading and cyclic lateral loading were carried out to explore their seismic performances. All specimens were evaluated by the failure modes, hysteresis characteristics, strength and stiffness degradation, energy dissipation capacity and ductility. The effects of section shape, stirrup spacing, axial compression and concrete strength of cast-in-place inner-part were investigated in details. The experiment results indicated that the PPSRC columns exhibited more satisfactory seismic behavior than the HPSRC columns in terms of hysteretic behavior, strength degradation, ductility and energy dissipation, while their bearing capacities were almost identical under low axial compression. Steel fibers could effectively prevent the cracked concrete from spalling, therefore, the encased steel shape was efficiently confined by the surrounding concrete during the entire test process. Higher stirrup ratio and lower axial compression of the column leaded to more satisfactory energy dissipation capacity, stiffness degradation and higher ductility. Based on the plastic stress theory, the seismic bending moment capacity analysis was conducted, and the results obtained form the formulas agreed well with those from the experiments. [ABSTRACT FROM AUTHOR]

A dissipative connector device, consisting of a steel plate folded at right angle along three lines to get a W-shaped profile, is proposed for the safe fastening of the horizontal cladding panels of new or existing precast structures under seismic action. Experimental tests are carried out to characterize the hysteretic behavior of the connector device. Different technological features, restraint conditions, and loading protocols are considered. Nonlinear hysteretic models are validated against the results of pseudo-dynamic tests on a full-scale prototype of precast building with cladding panels. Guidelines for the design of the dissipative connector device are provided. [ABSTRACT FROM AUTHOR]

Summary: Within the last decades, simplified methods alternative to dynamic nonlinear analysis have been developed to estimate the seismic performance of structures toward a performance‐oriented design. Considering drift as the main parameter correlated with structural damage, its estimation is of main importance to assess the structural performance. While traditional force‐based design deals with calibrated force reduction factors based on the expected structural ductility, other methods are based on the definition of a viscous damping factor defined as a function of the expected energy dissipated by the structure. An example is the capacity spectrum method. This method can be applied even without any a priori calibration or designer arbitrariness. This allows considering several peculiarities of the seismic behavior of precast structures, which may be influenced by nontraditional hysteresis of connections and members, interaction with the cladding panels, P‐δ effects, etc. The paper aims at verifying the soundness and accuracy of this method through the comparison of its predictions against the results of cyclic and pseudodynamic tests on precast structures, including single‐ and multistory buildings either stiff or flexible, obtained on full‐scale building prototypes tested within the framework of recent research projects (namely, “Precast Structures EC8,” “Safecast,” and “Safecladding”). Two simple methodologies of determination of the equivalent viscous damping from a force‐displacement cycle, based on the dissipated energy in relation to 2 different estimates of the elastic strain energy, are addressed and compared. Comments on the possible use of this procedure for the estimation of the seismic performance of precast structures are provided. [ABSTRACT FROM AUTHOR]

Seismic performance-based design approach is currently implemented in modern building codes. Design requirements and provisions ensure an adequate structural performance under different intensity levels of seismic action. However, the probability of attainment of a performance level is implicitly considered in the code design approach (provisions and requirements); for instance, the minimum requirements in concrete structures cannot be simply correlated to the probability of collapse of the building as well as to its overall structural response. The aim of this work is to assess the vulnerability with respect to the collapse limit state of industrial single-story RC precast buildings designed according to the current Italian seismic code. The comparison between the Italian code and the Eurocodes is provided throughout the paper. A parametric study is performed by investigating the safety against the collapse of 40 RC single-story precast structures. Multi-stripe analyses are performed by non-linear dynamic analyses at 10 intensity levels. The fragility of the structures is defined by means of the incremental N2 method, which has been demonstrated to be a suitable method for evaluating the collapse capacity of single-story precast buildings. The results demonstrate that the buildings are safe against the collapse mainly because of the structural overstrength with respect to seismic actions. The modelling assumptions are also validated in order to demonstrate the negligible influence of the cracking on the collapse as well as the importance of the geometrical nonlinearities for precast buildings. [ABSTRACT FROM AUTHOR]

Previous research projects and post-earthquake field observation showed that dry-assembled precast frame structures with hinged beams and cantilever columns restrained at their base, if correctly designed and detailed, can attain good seismic performance, mainly due to their flexibility and robustness. Their seismic design is often conditioned by the need of reducing their flexibility by increasing the cross-section of the columns, which, due to minimum reinforcement requirements, results in their over-strengthening. High flexibility may also induce displacement compatibility issues with non-structural elements. The paper concerns the proposal of an innovative enhanced structural frame system, based on the adaptation of hinged beam-column joints into rigid through the activation of special mechanical connection devices performed after the installation of the slab. While keeping all the benefits of the dry prefabrication, the resulting moment-resisting frame is provided with enhanced redundancy and stiffness. A design comparison among three precast frames with similar geometries and different static schemes shows how the joint adaptation can be exploited to optimise the structure by modifying the distribution of bending moment. The results of dynamic non-linear analyses on a three-storey precast structure with adaptable joints tested as a part of the SAFECAST research programme show the seismic performance of this system through different static schemes, and the comparison with the experimental results provides information about the validity of the models and the effectiveness of the technological solutions employed. [ABSTRACT FROM AUTHOR]

In this study, industrial single-story RC precast buildings are investigated. Twenty-four case studies have been considered, in which the column height, the beam spans and the seismic hazard level are varied. The seismic design of the selected case studies is performed according to the Italian building code and additional technical documentation. Three-dimensional nonlinear models are defined to perform static and dynamic analyses for the seismic assessment of the selected case studies. Demand/capacity ratios in terms of the selected engineering demand parameters are computed for ten increasing values of the seismic input return period. [ABSTRACT FROM AUTHOR]

Despite the long series of European research projects that has led to the setting of fully reliable seismic design criteria for precast structures, recent earthquakes have shown that a weak point still exists in the proportioning of the connection systems of cladding wall panels. Following this finding, this paper outlines an organic setting of the design problem of precast concrete structures including cladding-structure interaction and describes three possible solutions, namely, the isostatic, integrated, and dissipative systems. The related fastening arrangements, with the use of existing and innovative connection devices, are also described. This paper comments on the results of the pseudo-dynamic and cyclic tests performed at ELSA Laboratory of the European Joint Research Centre of Ispra (Italy) on a full-scale prototype of precast structure. The conception and the experimental performance of the structure with nine different configurations of either vertical or horizontal wall panel claddings are presented. The analysis of the results highlights the effectiveness of the different solutions in a comparative way. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Steel angles are extensively used to connect concrete floor/roof elements to the supporting beam in typical dry-assembled precast frame structures widely diffused in Europe and other parts of the world. These connections allow for relative rotations of the floor element in its vertical plane and restrain their relative displacement, avoiding possible loss of support and consequent fall of the floor element when the structure is subjected to lateral load. The diaphragm behavior of the precast decks relies on these floor-to-beam connections. Their postaddition to unconnected floor-to-beam joints of existing buildings is a typical seismic retrofit intervention. All these applications are often made without any adequate information about the main structural parameters of the connections due to lack of experimental or theoretical knowledge. An experimental campaign has been performed at Politecnico di Milano within the framework of the Safecast and ReLUIS research projects with the scope of characterizing the mechanical behavior of postinserted floor-to-beam connections made with hot-rolled angles, cold-formed angles, and welded sockets in the direction parallel to the floor element. The results of monotonic local tests on connectors and on the bolted connection with the floor rib and of cyclic and monotonic subassembly tests allowed the determination of the main structural parameters of the joints, including elastic stiffness, strength, displacement capacity, and hysteretic shape. [ABSTRACT FROM AUTHOR]

The stability of precast concrete wall panels under seismic action can be ensured by means of dissipative systems of panel-to-panel connections that allow to control the level of forces and limit the displacements. This paper deals with a connection system consisting of friction-based devices inserted into appropriate recesses within the joints between vertical or horizontal panels. The results of experimental tests carried out on single connectors, as well as on structural sub-assemblies consisting of two full scale panels, are presented. The technological choices of materials and components that ensure a stable hysteretic behaviour of the devices are discussed. The effectiveness of the devices in improving the seismic performance of precast buildings under seismic action is also shown based on the results of cyclic and pseudo-dynamic tests on full-scale structural prototypes. [ABSTRACT FROM AUTHOR]

The Displacement Based Design (DBD) methodology for precast concrete frame structures with not-emulative connections is investigated herein. The seismic design procedure is applied to both single-storey and multi-storey structures. Industrial and office buildings, warehouses and commercial malls with a structural layout typical of the European market are considered: cantilever columns resting on isolated footings connected at the floor level to pre-stressed precast beams, supporting pre-stressed precast concrete floor or roof elements. The need to control the lateral seismic displacement is dictated by the high flexibility of these structures, which in turn is associated to the structural scheme and to the inter-storey height. Starting from the general displacement based design procedure, the paper focuses on how properly taking into account the influence of column-to-foundation and beam-to-column precast connections; expressions and procedures are developed to determine the yield curvature, the equivalent viscous damping, the effective height and the effective mass of the single degree of freedom substitute structure adopted in the DBD procedure. The proposed procedure is applied to selected case studies and validated through non-linear time history analyses, showing the ability of the design procedure in controlling lateral displacements. [ABSTRACT FROM AUTHOR]

Silicone sealant is usually interposed between panels of precast façades. In ordinary cladding panel configurations, relative sliding between panels occurs under lateral actions. The shear drifts and consequent stresses arising in the silicone strips may lead to a significant increase of the load demand in the cladding panel connections and affect the seismic behaviour of the structural system. This paper presents the results of experimental tests and numerical analyses carried out to clarify the role of the silicone sealant on the seismic response of precast structures with cladding panels. An experimental campaign including monotonic and cyclic tests on both silicone strips applied to small concrete blocks and two panel sub-assembly sealed with silicone, has been developed at Politecnico di Milano. Furthermore, cyclic and seismic pseudo-dynamic tests on a full-scale prototype of precast building with cladding panels sealed with silicone, have been performed at the Joint Research Centre of the European Commission. The results of the experimental tests are presented and compared with the results of numerical simulations. Some recommendations for seismic design of precast frame structures with cladding panels, considering the effect of silicone sealant, are finally provided. [ABSTRACT FROM AUTHOR]

The SAFECLADDING Project was aimed at improving the connection systems between cladding panels and precast RC buildings in seismic-prone areas. Three design criteria have been assessed: isostatic , dissipative and integrated . They can be realised using different strategies, which are represented by several test setups within the experimental campaign. The paper describes the results obtained with vertical panels arrangement and the comparison with the bare frame, which is the reference for the current design practice that considers panels like non-structural elements. The mock-up and the test sequence were designed to assess all setups with a single frame structure. The mock-up was a one-storey building, made by two parallel frames with two bays and square columns, inserted into pocket plinths. The building was designed for earthquake actions according to the Eurocode 8. Each setup was assessed using increasing levels of action, either with cyclic or pseudo-dynamic tests. The latter were performed both for serviceability and ultimate limit states. The experimental programme for vertical-panels and the bare-frame arrangement involved ten different setups, resulting in a total of twenty-eight tests. As for the isostatic criterion, the results confirm that considering panels as simple masses without stiffness is far from the real system behaviour, even using apposite devices to uncouple panels and frame displacements. In fact, despite a previous and positive experimental qualification, several devices failed in operative conditions tests. Conversely, the integrated criterion requires to bear high loads, transferred by the frame through connections, which becomes the weak point for this configuration, as demonstrated by different failures of bolts and connections. The reliability of the dissipative criterion has been confirmed by twelve tests completed without any damage. This solution in fact combines lower relative displacements with limited loads within connections, avoiding both the compatibility problems and excessive forces. [ABSTRACT FROM AUTHOR]

• The interaction of the roof's horizontal diaphragm with the structural and non-structural elements influences the seismic behaviour of industrial buildings. • It was obtained a correlation between the stiffness required for a rigid behaviour at the roof level in terms of the shape of the building. • The consideration of a rigid diaphragm tends to produce a more realistic seismic behaviour of the overall structure. • The contribution of facade cladding wall panels significantly influences the seismic behaviour of the building, especially for high-rise buildings. The seismic behaviour of precast reinforced concrete industrial structures has been extensively investigated in recent decades, especially after the damage caused by recent earthquakes. The interaction of the roof's horizontal diaphragm with the structural and non-structural elements can influence the seismic behaviour of these buildings. Thus, the present study aims to investigate this interaction, through nonlinear static and dynamic analyses using a simplified macro element to simulate the behaviour of cladding panels and an equivalent truss approach to simulate the roof in-plane stiffness. The analyses were performed on several structural models considering the current European single-storey precast reinforce concrete industrial building stock, with or without cladding wall panels, and with rigid or flexible diaphragm roof. Despite the uncertainties associated with the ability of common roof systems to ensure a rigid diaphragm, the analyses allowed the establishment of a correlation between the buildings generic properties and the roof horizontal stiffness required to approach a rigid diaphragm effect. In general, the results show that the consideration of a rigid diaphragm in numerical models may tend to produce a more realistic seismic behaviour of the overall structure. Furthermore, the contribution of facade cladding wall panels significantly influences the seismic behaviour of the building, especially for high-rise buildings. [ABSTRACT FROM AUTHOR]

The use of precast reinforced concrete elements is rapidly increasing since this technique has several advantages over traditional cast-in-situ structural members such as lower manufacturing time and costs and a better quality control. Nevertheless, cast-in-situ solutions intrinsically allow building moment-resisting frames, a behavior that is usually hard to achieve using precast elements. In this paper a technical solution able to offer both high strength and ductility, simplicity of construction of the prefabricated elements and ease of assembly on site is presented. The solution realizes the continuity between beam and column by means of loop splices and cast-in-place concrete with steel fibers to improve the ductility of the concrete struts in the wet joint. The connection has been experimentally tested and compared to an analogous cast-in-situ one. The experimental results confirmed its good structural performances in terms of strength and ductility. Numerical investigations tuned on the basis of the experimental results allowed the improvement of the design to achieve reduced column damages for higher drift values while maintaining practically unchanged structural performances. [ABSTRACT FROM AUTHOR]

Current design approaches consider cladding panels (CPs) in precast RC buildings as non-structural elements not interacting with the frame. Frame/CP connections are typically designed only for wind or seismic actions perpendicular to the panel plane; unrestrained displacements in the panel plane are presumed. Past seismic events have clearly demonstrated the inadequacy of this design approach. CPs do in fact interact with the frame, modifying the response of buildings subjected to seismic action. This means that substantial and unexpected forces act on the connections and may lead to connection failure. Evidence of such out-of-plane forces in joints arising in buildings with deformable roof diaphragms is given here. This work proposes using CPs as structural elements to enhance the seismic performance of framed industrial buildings. If the friction acting between the panels is taken into account, CP walls become part of the resisting structure, leading to a dual frame/wall system. This concept can be used both in the design of new buildings and the retrofitting of existing ones. The case study reported here was conducted with CPs arranged horizontally and with pinned connections. We show that the results are highly sensitive to the assumed friction coefficient, and also that they differ substantially from analytical design values obtained disregarding friction effects. Friction between panels is known to be unpredictable, especially when structures are subjected to seismic movement with a strong vertical component. The consequence is that forces and displacements in framed buildings are random in a way which cannot be accepted in structural design. This work therefore proposes control of friction magnitude with suitable devices between panels: CPs can act as resistant and dissipative shear walls in industrial buildings, and are effective and relatively low-cost. [ABSTRACT FROM AUTHOR]

Given the catastrophic consequences following progressive collapse, designs to mitigate such events are of great interest to both the academic and engineering communities. This has led to the development of numerous design guidelines across the world to facilitate such efforts. Many authoritative papers were prepared, especially in the past decade, to evaluate the reliability of existing design methods for progressive collapse assessment. The deficiencies in existing guidelines on critical issues, such as dynamic effects, tie force and integrity approaches, slab effects, and acceptance criteria, are addressed based on the findings from some significant technical papers. Recommendations are included to identify the current concerns on developing existing design guidelines and also present a state-of-the-art review of the proposed refinements. Potential areas for future research are also explored. [ABSTRACT FROM AUTHOR]

In this paper, the finite element model calibration of precast structures was investigated by considering ambient vibration test results. Two precast structures, an overpass and a precast production facility, were selected for investigation. The initial finite element models of these structures were developed by using SAP2000 software and the initial dynamic characteristics were determined. The experimental measurements were carried out by Operational Modal Analysis method under ambient vibrations, such as wind and traffic loads, and the exact dynamic characteristics were identified experimentally. During the ambient vibration tests, structural responses were measured on different points of these precast structures. Measurement time, frequency span and effective mode number were determined by the pretest investigations. The modal parameters were extracted from the collected signals by Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification techniques. At the end of the study, the analytical and experimental dynamic characteristics were compared with each other and the initial finite element models of these structures were updated by changing the stiffness coefficients of the connection joints. [ABSTRACT FROM AUTHOR]

During the recent severe seismic events, as L'Aquila (2009) and Emilia earthquakes (2012), the collapse of cladding panels system in precast buildings has been frequently observed due to their connection system failure. Such a damage have demonstrated the deficiency of the actual design approach, that considers cladding panels as non-structural elements, neglecting any interaction with the structure under bi-directional and dynamic seismic excitations. This paper investigates the influence of vertical cladding panels on the first vibration period of one-story precast concrete buildings, with floor rigid in its own plane. At this purpose, a bare structural elastic model and an innovative elastic model of the building with cladding system are implemented and a parametric study is performed. The results of the parametric study show a high influence of the panels on the first period of the analyzed buildings, as well as the inadequacy for this typology of buildings of the simplified relationship for computing the fundamental period proposed by some codes. More suitable formulas are proposed to evaluate the first period in a linear static analysis of one-story precast buildings, both in the case of bare buildings and of buildings with cladding system. [ABSTRACT FROM AUTHOR]

The seismic sequence which hit the Northern Italian territory in 2012 produced extensive damage to reinforced concrete (RC) precast buildings typically adopted as industrial facilities. The considered damaged buildings are constituted by one-storey precast structures with RC columns connected to the ground by means of isolated socket foundations. The roof structural layout is composed of pre-stressed RC beams supporting pre-stressed RC floor elements, both designed as simply supported beams. The observed damage pattern, already highlighted in previous earthquakes, is mainly related to insufficient connection strength and ductility or to the absence of mechanical devices, being the connections designed neglecting seismic loads or neglecting displacement and rotation compatibility between adjacent elements. Following the vulnerabilities emerged in past seismic events, the paper investigates the seismic performance of industrial facilities typical of the Italian territory. The European building code seismic assessment methodologies are presented and discussed, as well as the retrofit interventions required to achieve an appropriate level of seismic capacity. The assessment procedure and retrofit solutions are applied to a selected case study. [ABSTRACT FROM AUTHOR]