Precast Frame Research Articles

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.

Mechanical connections of the precast concrete columns with detachable metal plates

SummaryThe aim of this study is to develop laminated metal plates for a moment connection of the precast concrete columns. Metal plates were proposed as a time‐ and cost‐saving alternative to conventional monolithic cast‐in‐place joints for connecting precast concrete frames. This study investigated the possibility of using mechanical joints for the connections of both steel‐concrete composite precast frames and reinforced concrete precast frames. A full erection test of precast columns connected with laminated metal plates was performed to demonstrate the efficiency and simplicity of the proposed method. It was shown that the use of the novel mechanical joints with steel plates significantly reduces construction time compared with the conventional monolithic assembly. The total precast column assembly time was approximately 10–20 min, eliminating pour forms and curing times required for the conventional concrete frames. This study also presents an analytical modeling of the proposed connection for multibay precast frames to explore the strains and stress exerted on the joints.

Moment-Rotation Response of Beam-Column Connections in Precast Concrete Structures

This paper provides an experimental investigation on the moment-rotation response of typical moment resisting beam-column connections, employing continuous negative bars consolidated with cast in place concrete over the precast beam and passing through grouted corrugated sleeves into an intermediate column. According to [1], the relative beam-column rotation is highly dependent on the elongation mechanism of the negative bars related to both the embedment length into the grouted sleeves and the development length over the beam end, being also inversely dependent on the vertical distance between the position of the top bars and the centre of rotation at end beam section. The flexural secant stiffness of the moment-rotation response is caused by a sum of the joint opening mechanisms at the beam-column interface and crack propagation within the connection zone, wherein the bond-slip at crack positions occurs prior to the first yielding of the negative bars. Therefore, the semi-rigid behaviour of the beam-column connections is associated with deformation mechanisms that occur at the SLS, but which also affects the global behaviour and stability analysis of precast frames at the ULS.Cruciform tests of full scale beam-column connections were carried out at the Precast Research Centre of the Federal University of Sao Carlos (Brazil), where 6 prototypes were studied varying the detailing of the positive connectors over the concrete corbel. The first pair of connectors employed elastomeric bearing pads with 2 vertical dowel bars, the second pair of connectors employed horizontal joints filled with grout with 2 vertical dowel bars and the last pair of connectors employed positive welded plates. The comparison between the experimental results showed that the smallest secant stiffness, which was obtained from the connector with elastomeric bearing pad, was corresponded to 89% and to 82% of the highest secant stiffness obtained for the connectors with welded plates and grouted joint, respectively. Therefore, the experimental results indicate that the major deformation mechanism within the beam-column connections is mostly dependent on the elongation of the top bars. Finally, a simplified analytical equation has been calibrated against the experimental results of the studied beam-column connections.

A NUMERICAL STUDY OF PRECAST BEAM-COLUMN MOMENT CONNECTIONS UNDER COLUMN REMOVAL SCENARIO

Precast concrete structures become widely used recently due to high quality of manufacturing as well as its good behaviour under gravity .However the most critical part in the precast structures is beam to column connections in precast frame system due to the different variables involved in the assemblages. In this paper a study is carried out on different wet beam column connections under column removal scenario to observe the behaviour of the connections due to progressive collapse. Different column removal locations with different frame arrangements is studied. The Applied Element Method is implemented in the study to construct a 3D detailed model of the studied connections by using Extreme Loading of Structures Software. The performance of the connections is presented in terms beam, column and joint behaviour. Maximum beam deflection, rotation and internal axial force, normal and shear stresses of the connection reinforcement as well as the column behaviour in terms of rotation and internal axial forces are discussed. From the results obtained an enhancement design is suggested for the failed connections and studied its effect in resisting the local failure due to column removal.

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.

An application of precast hybrid moment-resisting frames for seismic improvement

This paper presents an application of precast, hybrid, moment-resisting frames for improving the seismic safety of a standard five-storey residential building with a gravity-loaded, cast in situ reinforced concrete beam–column frame system. The non-linear mechanism of this new system is mainly governed by the opening and closing of discrete gaps at the interfaces of precast members. The improvement involved several research and development components, including quasi-static reversed cyclic loading tests, capacity design of hybrid frames, seismic performance evaluation of the entire building system using non-linear dynamic analysis, and cost comparisons of the original and proposed hybrid systems. Excellent seismic performance was demonstrated using each hybrid joint type; their force–deformation responses exhibited ductile stable hysteretic loops for up to 6% drift levels without severe damage. The hybrid frame building can withstand strong ground shaking (peak ground acceleration of 0·50g) without collapsing at minimal increased total cost (16·6%) compared with the cost of the original building.

Role of Soil–Structure Interaction on the Response of Precast RC Structures under Seismic Loading: Case Study

AbstractConsidering soil–structure interaction in structural modeling often plays an important role in the seismic design or retrofitting of buildings. In the present paper, soil–structure inertial interaction is analyzed with reference to a single-story precast frame concrete structure (typical of industrial buildings) founded on isolated footings. The analysis was carried out within the framework of a dynamic impedance method. Emphasis was placed on the application of such a method, originally conceived for the case of harmonic vibration in machine massive foundations, in seismic loading. The effects of considering the deformability of foundation soil in the seismic performances of the building are discussed. The adopted method sheds light on the potentialities of applying routine analyses to a great number of similar existing structures that need to be reinforced because they are located in regions of high seismic hazard.

Experimental investigation of dry mechanical beam–column joints for precast concrete based frames

SummaryThis paper proposes dry mechanical beam–column joints for fully restrained moment connections of concrete components. This novel joint can be used for reinforced concrete precast frames and steel–concrete composite precast frames. The new dry mechanical joint consists of extended steel plates with bolts designed to transfer tension and compression forces, providing fully restrained moment connections at the beam–column joint. The extended end plate with bolts introduced for column‐beam joint assembly was originally used in the steel moment frame, as introduced in AISC 358. This study developed similar but unique mechanical joint details for concrete frames in order to provide fully restrained moment connections for both steel–concrete composite precast frames and reinforced concrete precast frames. Experimental and analytical investigations were performed to verify the structural behavior of fully restrained moment connections for concrete components in order to identify the parameters that influence the structural behavior of dry mechanical moment concrete connections. These connections are expected to be used in modular offsite construction for buildings and heavy industrial plants. Copyright © 2016 John Wiley & Sons, Ltd.

Simulation study on dynamic response of precast frames made of recycled aggregate concrete

3-dimentional precast recycled aggregate concrete (RAC) finite element models were developed by means of the platform OpenSees to implement sophisticated nonlinear model subjected to seismic loads. Efforts were devoted to the dynamic responses (including dynamic characteristics, acceleration amplifications, displacements, story drifts) and capacity curve. In addition, this study extended the prediction on dynamic response of precast RAC model by parametric study of material properties that represent the replacement percentage of Recycled Coarse Aggregate (RCA). Principles and assumptions that represent characteristics of precast structure and influence of the interface between head of column and cast-in-place (CIP) joint on the stiffness of the joints was put forward and validated by test results. As a result, the comparison between simulated and tested results of the precast RAC frame shows a good correlation with most of the relative errors about 25% in general. Therefore, the adopted assumptions and the platform OpenSees are a viable approach to simulate the dynamic response of precast frames made of RAC.

Polygonal loop model for hysteretic behaviour of frame structures with recycled aggregate concrete

On the basis of shaking table tests on the recycled aggregate concrete (RAC) precast frame structure subjected to excitations of Wenchuan wave (WCW, 2008, N-S), El Centro wave (ELW, 1940, N-S) and Shanghai artificial wave (SHW), this study employed a new polygonal loop model (PLM) with its two core characteristics, that is, stiffness and strength degradation to describe the hysteretic behaviour of RAC frames. The implementation of the PLM model underwent different stages such as backbone curve, pivot points and unloading/reloading rules. The validation by shaking table tests on the precast RAC frame and application of the PLM to one cast-in-place RAC frame structure revealed that the hysteresis loops generated by the proposed PLM model not only traced the hysteretic trend but also fitted well with the tested hysteretic curves. Given these findings, it may be concluded that the new PLM model can be used to predict the seismic behaviour of RAC frame structures.

CAST-IN-PLACE BUILDING FRAME AND ITS FEATURES AT SEPARATE LIFE CYCLES

Modern intensive development of precast-cast-in-place construction has led to creation of a wide range of various constructive systems of buildings during the last 100 years. They allow constructing buildings with best account of the requirements of functionality, architectural expressiveness, production possibilities of construction companies, etc. However in spite of this development both precast and cast-in-place housing construction has its peculiarities, positive and negative ones. The constructive systems of precast monolithic buildings existing at the moment are based on the required mutual deformation of prefabricated reinforced and cast iron reinforced concrete at the stage of a building construction and at the stage of its use as well. Having refused from this rule, the authors of this article have introduced a constructive system of a precast monolithic building able to bear loads, developing at the stage of erection (due to completion of a precast frame) and at the stage of use (due to completion of a precast monolithic frame). The offered construction of a precast monolithic building frame allows efficiently using the advantages of precast and cast-in-place construction minimizing their disadvantages and it also fully corresponds to the obligatory requirements to buildings. The corresponding patents are obtained.

Shake Table Test on Seismic Response of a Precast Frame with Recycled Aggregate Concrete

A precast frame model made of Recycled Aggregate Concrete (RAC) was constructed with precast beams, columns and Cast-In-Place (CIP) joints. Then a shaking table test was carried out with three types of earthquake ground motions, namely Wenchuan, El Centro and artificial Shanghai waves. Based on the shaking test, structural responses such as dynamic characteristics, cracking and failure pattern, seismic responses as well as the overall seismic performance of the model were analyzed and evaluated. The results indicate that the precast RAC frame structure has an adequate load bearing potential as well as ductility against moderate and severe seismic excitations. Therefore, the perfect combination of RAC and precast structures is feasible to apply and popularize precast RAC frame structures with mid-rise buildings in the seismic regions.

Seismic Behavior of Cast-in-Place and Precast Recycled Aggregate Concrete Frames: A Comparative Study

Shaking table tests were carried out on two recycled aggregate concrete (RAC) frames, one of which was cast-in-place (CIP) and the other was precast. The dimensions and reinforcements of the two structures were designed similarly for the purpose of comparing seismic performance. The comparative analysis of the structural behavior indicated that both the models performed favorably with respect to their capacity for seismic resistance and presented similar dynamic response tendencies in the elastic and early nonlinear stage. In the later elastoplastic stage, for the precast RAC frame, the deformation was relatively larger, the overall seismic capacity was lower and the stiffness degradation was faster compared to the CIP frame. A further analysis of the frame joints of the two frames was undertaken and it demonstrated that serious damage to the post-cast joints in the precast frame was the main reason for the inferior structural seismic behavior during earthquakes of high-level intensity.

Correlation of Stiffness and Natural Frequency of Precast Frame System

The main objective of this study was to obtain the correlation between the severity of damage to the stiffness of the frame in the format of its intrinsic dynamic properties, the natural frequency of the structural system at damaged and undamaged state. In this research, a laboratory test was performed on the precast post-tension frame of a similar dimension and strength specification to Jabatan Kerja Raya (JKR) school buildings. The modal frame is a reduced in scale of 1 to 5 and subjected to cyclic lateral loadings and monitored its frequency through vibration test. The vibration test was performed at each end of the cycle of a lateral pushover test. The vibration data was recorded by accelerometers due to external forced vibration to assess its natural frequency, mode shapes and damping values of the system. This research found that there is a physical tangible relationship between natural frequency changes and stiffness in the frame. The results showed that as the severity of damage increases, the natural frequency of the frame decreases significantly, indicating that softening of the system that lead to a favorable ductility for earthquakes.

Low Reversed Cyclic Loading Test for New Precast Concrete Beam to Column Connection

On the basis of the domestic and overseas scholars’ research, it is innovative to put forward a new precast frame beam-to-column connection. One full-scale beam-to-column connection in a precast concrete（PC）frame and a beam-to-column connection in a cast-in-place concrete structures were tested under uni-directional cyclic loading that simulated earthquake-type motions. The new-type beam-to-column joint in a precast concrete frame consisted of cast-in-place columns and precast beams. Test results showed that（a）The property and action of precast connections are similar to the cast-in-place connection, it showed that both precast connections and cast-in-place connection have similar seismic performance; (b) The cracking load of precast connection are similar to the cast-in-place connection; (c) All the columns of all specimens did not destroy, it illustrate that it conform to the strong column weak beam. (d) In this experiment test, because the control factor use the bending capacity of beam, it also play the same plastic hinge mechanism as the traditional component. All the longitudinal reinforcement destruction ahead of stirrup in beams, which should be confirmed the guiding ideology of strong shear weak bending. On the basis of the test results, design considerations for the beam-to column connection were recommended.

Study on Seismic Behavior of Self-Centering Precast Frame

Self-Centering structure is a kind of new structure, which aims for reducing the residual deformation of structure after the earthquake. In order to research the Seismic Behavior of Self-centering Prefabricated concrete frame, a new joint applied with prestressed tendons and a traditional joint are designed in this paper with the finite element software ABAQUS. The seismic performances of them are contrastively analyzed. The new joint is found to have better self-centering capacity. Then two plane frame models are analyzed. The result shows that the frame applied with prestressed tendons has some capacity of self-centering and enough energy dissipation effects.

Formula of Unbonded Tendon Stress Increment Based Performance

Unbonded tendon stress calculation of unbonded precast concrete structure is defferent from prestressed concrete structure, as tendon strain caused by the external load is not in accordance with relevant sections of the concrete strain obtained. As the deformation of unbonded tendons are not subject to the deformation of plane-section assumption, therefore, arise due to external loads of unbonded tendon stress calculation is more complex. In this paper, based on theoretical analysis and derivation, the pre-stress deformation of the unbonded steel stress formula was given, this can provide more scientific basis for the stress Analysis of unbonded precast frame structure.

Mathematical Model of Hybrid Precast Gravity Frames for Smart Construction and Engineering

The structural stability, constructability, economic feasibility, environmental-friendliness, and energy efficiency of hybrid composite frame systems have been demonstrated by practical application and research. A hybrid composite frame system combines the economy of precast concrete structures with the constructability of steel frame structures, including erection speed. Novel composite frames will ultimately maximize the efficiency of structural design and facilitate construction. This paper presents hybrid precast frames, which are precast composite frames based on a simple connection between precast concrete columns and beams. The hybrid precast frames designed to resist gravity loading consist of PC columns, PC beams, and steel inserted in the precast members. Steel sections located between the precast columns were simply connected to steel inserted at each end of the precast beams. Dynamic analysis of a 15-story building designed with the proposed composite frame was performed to determine the dynamic characteristics of a building constructed of hybrid frames, including frequencies and mode shapes.

Research on recycled concrete and its utilization in building structures in China

Large quantities of construction and demolition (C&D) building waste are being generated as a result of rapid urbanization and natural disasters in China. An increasing awareness of environmental protection is escalating C&D waste disposal concerns. This paper presents a brief introduction to current shaking table test research in China on structures built with recycled aggregate concrete (RAC). Test structures include a cast-in situ frame model, a precast frame model and a block masonry building. The test results prove that it is feasible to use RAC as a structural material in seismic areas, with recommended modifications and proper design, especially in low-rise structures. This paper also presents several successful applications of RAC in civil and structural engineering projects in China, which will serve to promote RAC as a global ecological structural material.

The development of modularized construction of enhanced precast composite structural systems (Smart Green frame) and its embedded energy efficiency

Precast structural systems demonstrate outstanding economy compared to steel structures, but the construction speed is not as fast as steel construction, preventing precast structural systems from being widely used. This results from the difficulty in installing beams for lateral braces during erection. The structural system is proposed for the easy and simple connections of column-beam units to beam units to form lateral braces during erection. Vertical steel sections with brackets are inserted in between upper and lower precast columns at the joint level. The column-beam unit is lifted in sites to be assembled with steel sections inserted at both ends of the precast beam unit. The introduction of the steel section both in column-beam and beam units allows for precast frames to be erected as similarly as steel frames providing a proper lateral resisting frame to prevent lateral instability during erection. The hybrid construction based precast composite frames introduced in this paper adds to the economy of using precast concrete structures with steel erection speed. This paper also presents the embedded energy efficiency of the proposed precast concrete frames based on the material, structure and construction hybrid characteristics.