An effective simplified model of composite compression struts for partially-restrained steel frame with reinforced concrete infill walls

To resolve the issue regarding inaccurate prediction of the hysteretic behavior by micro-based numerical analysis for partially-restrained（PR）steel frames with solid reinforced concrete（RC）infill walls,an innovative simplified model of composite compression struts is proposed on the basis of experimental observation on the cracking distribution,load transferring mechanism,and failure modes of RC infill walls filled in PR steel frame.The proposed composite compression struts model for the solid RC infill walls is composed ofαinclined struts and main diagonal struts.Theαinclined struts are used to reflect the part of the lateral force resisted by shear connectors along the frame-wall interface,while the main diagonal struts are introduced to take into account the rest of the lateral force transferred along the diagonal direction due to the complicated interaction between the steel frame and RC infill walls.This study derives appropriate formulas for the effective widths of theαinclined strut and main diagonal strut,respectively.An example of PR steel frame with RC infill walls simulating simulated by the composite inclined compression struts model is illustrated.The maximum lateral strength and the hysteresis curve shape obtained from the proposed composite strut model are in good agreement with those from the test results,and the backbone curve of a PR steel frame with RC infill walls can be predicted precisely when the inter-story drift is within 1%.This simplified model can also predict the structural stiffness and the equivalent viscous damping ratio well when the inter-story drift ratio exceeds 0.5%.

Study on the effect of the infill walls on the seismic performance of a reinforced concrete frame

Motivated by the seismic damage observed to reinforced concrete （RC） frame structures during the Wenchuan earthquake, the effect of infill walls on the seismic performance of a RC frame is studied in this paper. Infill walls, especially those made of masonry, offer some amount of stiffness and strength. Therefore, the effect of infill walls should be considered during the design of RC frames. In this study, an analysis of the recorded ground motion in the Wenehuan earthquake is performed. Then, a numerical model is developed to simulate the infill walls. Finally, nonlinear dynamic analysis is carried out on a RC frame with and without infill walls, respectively, by using CANNY software. Through a comparative analysis, the following conclusions can be drawn. The failure mode of the frame with infill walls is in accordance with the seismic damage failure pattern, which is strong beam and weak column mode. This indicates that the infill walls change the failure pattern of the frame, and it is necessary to consider them in the seismic design of the RC frame. The numerical model presented in this paper can effectively simulate the effect of infill walls on the RC frame.

Effects of timber infill walls on the seismic behavior of traditional Chinese timber frames

This study investigates the enhanced effect of timber infill walls on the seismic behavior of traditional Chinese timber frames.Two 1/2 scaled traditional Chinese timber infill walls(TIWs),two 1/2 scaled timber frames with timber infill walls(TFTIWs)and one 1/2 scaled timber frame(TF)were fabricated and tested under low-cyclic reversed loading.The failure modes,strength,stiffness,and energy consumption capacity of the TIWs and the TFTIWs were obtained,and the effects of the TIWs on the seismic performance of the TFTIWs were investigated.The results showed that the TIWs can increase the stiffness and ultimate bearing capacity of the TF,up to 60%and 80%,respectively.The strength degradation coefficient of the TFTIWs was slightly higher than that of the TF when the inter-story drift ratio exceeded 0.02 rad,and the TIWs helped to mitigate the strength degradation of the TFTIWs.It was also found that the TFTIWs had a higher cumulative energy dissipation when compared with the TF(up to a 60%increase),indicating the TIWs had reasonably good energy dissipation capacity.When the TIWs generated a solid contribution to the carrying capacity and energy dissipation of the TF,the lateral drift thresholds were 1/100 and 1/43 of the column height,respectively.Furthermore,the TIWs and TFTIWs presented a good ductility,and the TIW could effectively reduce the pull-out amount of the tenon from the mortise of the TF;however,the TIWs had little influence on the stiffness degradation level or improvement of the ductility of the TF.

Mechanical properties characterization of different types of masonry infill walls

It is remarkable,the recent advances concerning the development of numerical modeling frameworks to simulate the infill panels'seismic behavior.However,there is a lack of experimental data of their mechanical properties,which are of full importance to calibrate the numerical models.The primary objective of this paper is to present an extensive experimental campaign of mechanical characterization tests of infill masonry walls made with three different types of masonry units:lightweight vertical hollow concrete blocks and hollow clay bricks.Four different types of experimental tests were carried out,namely:compression strength tests,diagonal tensile strength tests,and flexural strength tests parallel and perpendicular to the horizontal bed joints.A total amount of 80 tests were carried out and are reported in the present paper.The second objective of this study was to compare the mechanical properties of as-built and existing infill walls.The results presented and discussed herein,will be in terms of strain-stress curves and damages observed within the tests.It was observed a fragile behavior in the panels made with hollow clay horizontal bricks,without propagation of cracks.The plaster increased the flexural strength by 57%.

Performance of masonry enclosure walls:lessons learned from recent earthquakes

This paper discusses the issue of performance requirements and construction criteria for masonry enclosure and infill walls. Vertical building enclosures in European countries are very often constituted by non-load-bearing masonry walls, using horizontally perforated clay bricks. These walls are generally supported and confined by a reinforced concrete frame structure of columns and beams/slabs. Since these walls are commonly considered to be nonstructural elements and their influence on the structural response is ignored, their consideration in the design of structures as well as their connection to the adjacent structural elements is frequently negligent or insufficiently detailed. As a consequence, nonstructural elements, as for wall enclosures, are relatively sensitive to drift and acceleration demands when buildings are subjected to seismic actions. Many international standards and technical documents stress the need for design acceptability criteria for nonstructural elements, however they do not specifically indicate how to prevent collapse and severe cracking, and how to enhance the overall stability in the case of moderate to high seismic loading. Furthermore, a review of appropriate measures to improve enclosure wall performance and both in-plane and out-of-plane integrity under seismic actions is addressed.

Seismic performance evaluation of an infilled rocking wall frame structure through quasi-static cyclic testing

Earthquake investigations have illustrated that even code-compliant reinforced concrete frames may suffer from soft-story mechanism.This damage mode results in poor ductility and limited energy dissipation.Continuous components offer alternatives that may avoid such failures.A novel infilled rocking wall frame system is proposed that takes advantage of continuous component and rocking characteristics.Previous studies have investigated similar systems that combine a reinforced concrete frame and a wall with rocking behavior used.However,a large-scale experimental study of a reinforced concrete frame combined with a rocking wall has not been reported.In this study,a seismic performance evaluation of the newly proposed infilled rocking wall frame structure was conducted through quasi-static cyclic testing.Critical joints were designed and verified.Numerical models were established and calibrated to estimate frame shear forces.The results evaluation demonstrate that an infilled rocking wall frame can effectively avoid soft-story mechanisms.Capacity and initial stiffness are greatly improved and self-centering behavior is achieved with the help of the infilled rocking wall.Drift distribution becomes more uniform with height.Concrete cracks and damage occurs in desired areas.The infilled rocking wall frame offers a promising approach to achieving seismic resilience.

A Theoretical Study the Effect of Openings in Infill Wall Panels on the Behavior of Structures

Two dimensional,reinforced concrete building frames built on raft foundation and having infill wall panels with openings in them are analysed using the direct stiffness method.Beams and columns are modelled by beam column elements.Wall panels are modelled by plane stress finite elements.The raft foundation is modelled by uniaxial finite elements.The soil is modelled as half space model.Openings in wall panels are introduced by using fictitious beams between real floor beams. A computer program is written to carry out the static analysis and do the necessary comparison to show the effect of openings on the structural behavior.

Shaking test research on connection modes between block infill wall and frame beam

In order to achieve an optimal anti-seismic behavior,or rather stability,the out-of-plane stability of infill wall in frame has been researched with the shaking test of four sets of two-layer infill wall,in which four different connection modes of filled with inclined bricks on the top,disconnection,flexibility and semi-flexibility were adapted.The acceleration and displacement response of the specimens were analyzed under the seismic load.Also,some feasible connection modes were gained by comparing the response of infill walls.Finally,the calculation of earthquake of infill wall was held.The results showed that seismic responses of the infill walls whose connect with frame in form of flexibility and semi-flexibility modes are weaker than others obviously,and their integrality is better.Thus the conclusion could be drawn that out-of-plane stability of the specimens with connection modes of flexibility and semi-flexibility are better than those with the connection modes of filled with inclined bricks on the top and disconnection.The research results can provide evidence for establishing specifications and directing the construction and therefore help reduce the casualties and property loss caused by earthquake disasters.

Comparative Study on Diagonal Strut Model of Infill Wall

The equivalent diagonal strut models of infill wall mainly include the single strut model and multi-strut model.Firstly,several equivalent strut models and their characteristics are introduced in this paper.Then,model analysis and pushover analysis are carried out on infilled frame models with the aid of the software SAP2000.Two typical single strut models and a typical three-strut model are used to simulate the panel of the frames respectively.It is indicated that the period reduction factor of the frame with a three-strut model is close to the value recommended by the current code.The infill wall has great influence on the overall stiffness,bearing capacity and weak position of the structure.The stiffness and the bearing capacity of the infilled frame increase with the increase of the number of the infill walls.The unfilled story is the weak position of the infilled frame,and when the unfilled story at the bottom of the infilled frame,the seismic response of the upper infill layer decreases with the increasing of the number of unfilled story.

Performance evaluation of low-rise infilled reinforced concrete frames designed by considering local effects on column shear demand

The interactions between reinforced concrete(RC)frames and infill walls play an important role in the seismic response of frames,particularly for low-rise frames.Infill walls can increase the overall lateral strength and stiffness of the frame owing to their high strength and stiffness.However,local wall-frame interactions can also lead to increased shear demand in the columns owing to the compressive diagonal strut force from the infill wall,which can result in failure or in serious situations,collapse.In this study,the effectiveness of a design strategy to consider the complex infill wall interaction was investigated.The approach was used to design example RC frames with infill walls in locations with different seismicity levels in Thailand.The performance of these frames was assessed using nonlinear static,and dynamic analyses.The performance of the frames and the failure modes were compared with those of frames designed without considering the infill wall or the local interactions.It was found that even though the overall responses of the buildings designed with and without consideration of the local interaction of the infill walls were similar in terms the overall lateral strength,the failure modes were different.The proposed method can eliminate the column shear failure from the building.Finally,the merits and limitations of this approach are discussed and summarized.