Precast Frame Structures Research Articles

Shaking Table Test and Numerical Analysis of a Precast Frame Structure with Replaceable Box Connectors

Shaking Table Test and Numerical Analysis of a Precast Frame Structure with Replaceable Box Connectors

Experimental investigation into demountable dry connections for fully precast frame structures through shaking table tests

To fulfill the objective of reducing pollution and carbon emission while advancing the development of high-performance structural systems aligned with green building principles, an innovative demountable dry connection fully precast frame structure system was introduced in this paper. The structure is easy to assemble, can significantly enhance construction efficiency, and facilitates the upgrading and earthquake-damaged replacement of components during service. To comprehensively investigate the dynamic characteristics of this novel precast frame structure, a half-scale specimen structure was manufactured and tested on a shaking table. The seismic performance of the structure was evaluated by collecting and analyzing the data on acceleration, displacement, and strain, as well as observing the deformation and cracking of the structure. The results show that the structure performs well as designed with confined damage, and can achieve the performance target of withstanding minor earthquakes without damage and surviving severe earthquakes without collapsing. After experiencing strong earthquakes, the damage was concentrated on the concrete beams, and the damaged components were easy to demount and replace, which could extend the service life of the structure, ensure the sustainability of the structural seismic resistance, and present an effective solution for achieving environmentally conscious, green, and low-carbon construction practices.

Anchorage characteristics and their impacts on the seismic performance of HECC/RC composites external beam-column joint

In order to enhance the seismic performance and streamline the construction process, particularly in precast frame structures, steel-polyethylene hybrid fiber-reinforced engineered cementitious composites (HECC) is utilized to replace reinforced concrete (RC) in the external beam-column joint core area to form HECC/RC composite joints. In this study, to further alleviate rebar congestion, five no-stirrup reinforced HECC/RC composite external beam-column joints with reduced beam longitudinal rebar anchorage length (i.e., 6d-18d) in core area and one control RC specimen are designed and tested under cyclic loading. Experimental results indicate that anchorage failure occurs until the anchorage of the beam longitudinal rebar decreases to an extremely short length of 6d. In comparison with the control RC specimen, HECC/RC specimens display a reduced bond damage zone and superior bond behavior. Although relatively larger stress is transferred to the anchorage free end when anchorage length is 9d, the beam longitudinal rebar is still effectively anchored without significant slip, indicating that anchorage length of 9d in joint core area may be sufficient which needs further research. In addition, the ultimate bond strength of the rebar embedded in joint core area is lower than that observed in pullout test, underscoring the necessary of considering a safety factor in design anchorage length estimation. Lastly, the contribution of bonding condition on shear force transfer in joint core area is analyzed according to force transfer mechanism, which would promote the determination of the shear capacity of HECC joint. As the bonding damage expanded, the proportion of shear force resisted by truss mechanism decreases, emphasizing the crucial role of adequate anchoring in external joint.

Shaking table test of a dry-connection fully precast frame structure system

In view of the construction difficulties and ecological environment sensitivity of building construction in extremely cold and high seismic intensity areas, a new type of dry-connection fully precast frame structure system was proposed. The connections of the structure are easy to assemble, which can greatly improve the construction efficiency and provide convenience for the upgrading and replacement of components during service. In order to provide essential insights into the seismic performance of the dry-connection precast structure, a three-story precast frame structure specimen with a scale ratio of 1/2 was designed, constructed, and tested on a shaking table subjected to a series of ground motions with increasing seismic intensities. The connections of the specimen structure include beam-column joint, beam-floor joint and column-foundation joint, precast components were processed in the factory and assembled in the laboratory. The vibration characteristics, damage development, acceleration response and displacement response of the structure were investigated. The experimental results illustrated the excellent seismic performance of the structure with sufficient strength and relatively confined damage. The gradually decreasing frequency and increasing damping ratio were attributed to the slippage and plastic deformation of the connectors and the cracking of beam concrete. And the maximum story drift under rare earthquake of intensity 8 was within the design limit, indicated that the precast frame structure could achieve the performance target of no collapse under severe earthquakes. The data of this test provided support for further study on the design methods and numerical modeling of dry-connection fully precast frame structure systems.

Dynamic progressive collapse response of 3D monolithic precast concrete frame structures considering slab effects

The robustness of precast concrete frame structures to withstand extreme events like explosions, impacts, fires and terrorist attacks has attracted growing attention. With the understanding of the static progressive collapse performances of 2D precast frame structures, research on the dynamic responses of 3D precast frame structures is pressing and high in demand. To evaluate the influence of floor slabs on dynamic progressive collapse responses of 3D precast concrete frame structures, an experimental program consisting of a beam-column (PC) and a beam-slab-column (PCS) specimens was first designed, followed by the analysis of the working mechanisms to resist progressive collapse. The modeling techniques for 2D PC and PCS substructures were then proposed and validated using the test results. The numerical strategy was further extended to simulate the dynamic progressive collapse responses of 3D PC- and PCS-frame structures. Results show that, under various column loss scenarios, floor slabs significantly improve progressive collapse resistances of 3D frame structures. Moreover, it reveals that the floor slabs have a remarkable effect on reducing the nodal displacements and the dynamic amplification factors.

Soft omega joint for selective weakening of core walls in large precast commercial buildings

Commercial malls and similar large low-rise multi-storey building typologies are often constructed employing precast frame structures. Wall cores surrounding stairs and elevators often occupy a small area if compared to the frame area of large floors. Generally, these cores need to be decoupled from the frame structure, which is designated as the lateral load resisting system, given that, if rigidly connected to the frame, their high stiffness would draw seismic actions not compatible with their capacity or with economical/feasible foundation systems. The necessary core decoupling from the frame is hence generally made by horizontal structural joints of considerable width to avoid pounding, given the peculiar lateral flexibility of precast frame structures. However, these large joints are in reality highly complex, since they need to be compatible with internal finishes, pedestrian distribution and often fire compartmentation requirements. The present paper proposes an alternative to the use of decoupling frame-core joints consisting in deformable vertical joints made by omega-bent aluminum sheets and insulation strips to be inserted during production in the wall elements. The proposed omega-profiles, while avoiding the use of horizontal joints and keeping the fire compartmentation capacity of the core walls, selectively weaken the wall elements, lowering their stiffness and allowing for lateral deformation capacities compatible with that of frames. The mechanical behaviour of the proposed joint is assessed by lateral cyclic tests on full-scale wall panels with inner vertical voids surrounded by a solid frame connected with mechanical devices to the foundation beams. The comparison with the test results of a benchmark precast wall not provided with the proposed joints allows to quantify the enhanced flexibility and displacement capacity of the wall with omega joints and to interpret the role of the joints in modifying the resistance mechanism of the wall subjected to lateral loads. Moreover, the results of a non-linear numerical model based on an ideal joint behaviour allow to indirectly highlight the soft joint contribution to the wall behaviour under lateral load.

КОНСТРУКТИВНАЯ СИСТЕМА БЫСТРОВОЗВОДИМОГО ЗДАНИЯ ИЗ ИНДУСТРИАЛЬНЫХ ПАНЕЛЬНО-РАМНЫХ ЭЛЕМЕНТОВ

The paper presents a new structural solution of the precast-monolithic frame for prefabricated residential and civil buildings of various storeys manufactured from prefabricated industrial reinforced concrete elements. The precast frame structures include L-shaped and inverted U-shaped precast elements, installed in the longitudinal and transverse directions and forming a frame, hollow-core slabs and bracing perforated beams of the outer contour, on which fencing non-bearing wall structures are supported within each storey. The computational model of the precast-monolithic building frame was developed using different degrees of discretization at different stages of the analysis. This allowed to obtain both a general picture of structural system deformation in the limiting and over limit states caused by special and emergency actions, and a detailed picture of the stressed state in concrete and reinforcement of structural elements before and after cracking. The paper provides the results of the comparative analysis of the effectiveness of application of the proposed structural system in the mass construction as compared with the applied constructions of large-panel buildings. It has been shown that the application of the proposed structures of panel-frame elements allows considerably reduce the material capacity, cost and transportation expenses of the reinforced concrete frame by up to 30 %, ensuring the mechanical safety of the building.

Issues Regarding the Appropriateness of Using Precast Reinforced Concrete Frame Structures Compared to Monolithic Reinforced Concrete Frame Structures, in Office Buildings and Residential Buildings

Abstract Given the current context at national and European level in terms of reducing skilled labour force in constructions, as well as the high level of density and traffic in large cities, there is an increasing emphasis on the possibility of shortening the duration of building the structural frames on site, reducing the number of workers or even reducing the level of noise pollution. Thus, the introduction of precast technologies in the case of office buildings and residential buildings, with multi-storey frame structure, is becoming an increasingly pressing and topical issue. The purpose of this paper is to enable structural engineers, architects and potential investors to consciously choose the type of optimal structure, taking into account a number of technical and economic aspects. In this sense, in order to highlight the main advantages and disadvantages of using multi-storey precast reinforced concrete frame structures, a comparative case study will be carried out between a precast frame structure and a monolithic frame structure, respectively.

Experimental Research on the Seismic Characteristics of a Precast Frame Structure with a Viscous Damper

ABSTRACT Precast structures have become increasingly popular in recent years. However, the low seismic capacity of prefabricated structures is still a fraught issue in high seismic intensity regions. This paper aims to improve the structural seismic capacity of a precast concrete frame by employing a viscous damper. Two precast concrete frame specimens, with and without viscous dampers (PCFV and PCF), were produced and subjected to dynamic reversed cyclic loading tests. The experimental results showed that the viscous damper could improve the dynamic bearing capacity of the frames.

Seismic performance of prefabricated beam-to-column joint with replaceable energy-dissipating steel hinge

This study presents a novel energy-dissipating prefabricated joint for connecting beam to column in a precast frame structure. The joints are characterized by a replaceable steel hinge and a prefabricated steel tube confined joint core, providing advantages for precast concrete reinforced frames, such as complete assembly, damage control, and maintainability of the structure after an earthquake. The hysteretic behavior of the proposed prefabricated joint was studied through two tests. First, a full-scale prefabricated joint was tested under cyclic loading until failure. On the basis of the initial test, only four weakened dissipaters of the steel hinges in the prefabricated joint were replaced and the second test was conducted to investigate the restorable functional characteristics of the proposed prefabricated joints. For comparison, a reference monolithic joint was also tested. The experimental results demonstrate that the novel prefabricated beam-to-column joint displayed excellent hysteretic performance, and corresponding to the monolithic joint, the load-bearing, energy dissipation, and deformation capacity were improved. The damage of the prefabricated joint was concentrated on the weakened dissipaters of the steel hinges, indicating that the failure mode and damage degree of the prefabricated joint can be controlled. In the second test, the prefabricated joint exhibited similar hysteretic behavior to that of the first test; however, the initial stiffness was slightly lower. Therefore, the prefabricated joint can meet the replaceability requirement and achieve satisfactory beam-to-column joint function recovery after an earthquake.

Seismic behavior and design of repairable precast RC beam–concrete-filled square steel tube column joints with energy-dissipating bolts

The dry jointed precast frame structure has the potential in less reliance on wet concrete, low cost and repairability after earthquake. The seismic behavior of the novel precast dry connections with different beam end arrangements was studied in this work. For the precast specimens, the concrete-filled square steel tube (CFSST) column and RC beam were prefabricated, and field assembly was carried out by energy-dissipating (ED) bolts and unbonded prestressed tendons. Design equations were formulated according to the strong-column–weak-beam concept and the capacity design philosophy. The viability of the repair method of the precast internal beam–column connections after earthquake was explored. The joints were repaired by replacing the ED bolts and loaded again. The seismic indicators, such as ductility and energy dissipation capacity, were determined and compared. The results showed that the excellent structural characteristics and practical design method could ensure low damage to the joints except for the ED bolt yield. The new-type precast beam–column joints exhibited good hysteretic performance with high ductility factors greater than 5. After repair, the failure mode of the joints was controlled by the plastic hinge on the beam. The repaired joints had good strength stability, and the ultimate bearing capacity was the same as before repair. The ductility of the repaired joints was 13.29%–32.14% higher than before. The energy dissipation capacity could reach more than 1.2 times that of the cast-in-place concrete joints, which proved the feasibility of the repair method.

Performance of a Ductile Hybrid Post-Tensioned Beam-to-Column Connection for Precast Concrete Frames under Seismic Loads: A Review

The performance of precast concrete frame structures against seismic loads mainly depends on the beam-to-column connection. A ductile hybrid connection consists of unbonded post-tensioning steel and bonded reinforcement bars, both of which provide overall moment resistance to the frame. Post-tensioning steel acts as a restoring force which brings the structure back to its initial position upon unloading. Mild steel acts as an energy dissipator which yields in tension and compression. To evaluate the performance of precast frame structures, the structural engineer requires extensive knowledge of the complex nonlinear behavior of the connection. Standardization to mass produce is one of the benefits of precast construction, but with standardization in design there is severe risk. All previous earthquakes have clearly shown that continuous repetition of accepted practice without proper engineering review can lead to disaster. It is important to understand how different parameters of the connection influence the behavior and performance of the frame against seismic loads. The present study helps structural engineers and researchers with a detailed review of hybrid post-tensioned connections. This review is focused mainly on precast beam-to-column connections, studies on the development of hybrid connections, performance evaluations of hybrid connections, and the performance evaluation of precast frames with hybrid connections.

Tension-only ideal dissipative bracing for the seismic retrofit of precast industrial buildings

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.

Multi-Stripe Seismic Assessment of Precast Industrial Buildings With Cladding Panels

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.

Seismic Design of Precast Component Beam-Column Joints using Headed Anchors

Precast construction system ensures high degree of quality, safety, and accelerated construction practice in R.C structures. It is well established in non-seismic conditions where gravity loads are predominated. But it is hesitated to implement during seismic conditions by the effect of lateral loads. Most of structural failures in precast framed structures are associated with beam-column joints as the integrated joint system experience high shear, and moments by cyclic action of seismic loads. In this context, researchers found that the joint distortions in precast system is well associated with its location of beam-column sub-assemblage. In beam-column joints the connections are attributed to locate in D-regions (D:Discrete) and B-regions (B:Beam) where the force transfer mechanism follows by strut - tie method (STM) or flexure beam theory(FBT) respectively. This paper analyzed the seismic performance of “Component Based Precast Joints”[CBPJ] located in D& B regions. To meet the convergence requirements, the connection systems are detailed by mechanical couplers and headed anchors. Five numerical models of exterior beam-column joints representing two models (BM1,BM2) of B-region and three models (DM1,DM2,DM3) of D-region are developed and verified their seismic performance with monolithic joint system by non-linear finite element analysis using ABAQUS software .The results indicated that the use of headed anchors in precast joints are effectively contributed to seismic requirements of shear, ductility, stiffness and energy dissipation. Also the precast joints located in D & B regions resembling good performance of joint sustainability during moderate seismic conditions as monolithic system.

Experimental study on a precast beam-column joint with double grouted splice sleeves

The construction speed and quality of precast frame structures are greatly influenced by weld, tie, prestress, cast concrete requirements, etc. on site. To address these challenges, a precast beam-column joint connected by double grouted sleeves is proposed. This paper presents an investigation on seismic behaviour of the joint subjected to static and cyclic loadings. In total, six precast specimens with different assembly lengths, transition bar diameters and types of grouted sleeve and one cast-in-place control specimen were tested. Results show that the double grouted sleeve splices in joints perform well. The initial stiffness of prefabricated specimens is larger than that of the control specimen and the load bearing capacity of the prefabricated specimens is similar to that of the control specimen. As the transition rebar diameter increases from 16 mm to 18 mm, the energy dissipation ability of the prefabricated specimens is increased by 64.8% but is approximately 41% lower than that of the control specimen due to their relatively lower deformation capacity. Threads in the grouted sleeve have a negative impact on the deformation and energy dissipation abilities of the joints. The method for cast-in-situ joint is adequate for predicting the flexural capacity of precast joint connected by double grouted sleeves.

Diaphragm effectiveness of precast concrete structures with cladding panels under seismic action

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.

Seismic design and performance of dry-assembled precast structures with adaptable joints

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.

End support connection of precast roof elements by bolted steel angles

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.

Experimental investigation on the influence of silicone sealant on the seismic behaviour of precast façades

Silicone sealant is usually interposed between panels of precast facades. 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.