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

This 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.     

Life‐cycle cost assessment of mid‐rise and high‐rise steel and steel–reinforced concrete composite minimum cost building designs

The traditional trial‐and‐error design approach is inefficient to determine an economical design satisfying also the safety criteria. Structural design optimization, on the other hand, provides a numerical procedure that can replace the traditional design approach with an automated one. The objective of this work is to propose a performance‐based seismic design procedure, formulated as a structural design optimization problem, for designing steel and steel–reinforced concrete composite buildings subject to interstorey drift limitations. For this purpose, eight test examples are considered, in particular four steel and four steel–reinforced concrete composite buildings are optimally designed with minimum initial cost. Life‐cycle cost analysis (LCCA) is considered as a reliable tool for measuring the damage cost due to future earthquakes that will occur during the design life of a structure. In this study, LCCA is employed for assessing the optimum designs obtained for steel and steel–reinforced concrete composite design practices. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparative experimental study of full‐scale H‐subframe using a new industrialized building system and monolithic reinforced concrete beam‐to‐column connection

Industrialized building system (IBS) is a construction process that uses techniques, products, components or building systems that involve prefabricated components and on‐site installation. The structural behaviour of a prefabricated frame structure is widely affected by the specifications of the beam‐to‐column connection. The understanding on the real behaviour of a connection can be assessed by conducting full‐scale experimental tests. In this study, a new IBS hybrid steel–concrete connection in a full‐scale H‐subframe under monotonic loading is investigated. This innovative connection system, consists of precast concrete beam‐and‐column elements with embedded steel end connectors, is patented as Smart IBS. This paper reports the testing procedures and results of this semi‐rigid IBS beam‐to‐column connection to obtain the important attributes of the connection as well as its comparison with monolithic cast‐in‐place reinforced concrete model. The height of both H‐subframes is 3.3 m while the free length of the beam is 3.2 m. The incremental loads were applied as two point loads in one‐third and two‐third of the beam length. The characteristic relationships of the connection such as load to mid‐span deflection, strength, stiffness, ductility, failure modes and crack patterns are studied and compared between both structural systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Seismic behavior of T‐shaped steel reinforced concrete shear walls in tall buildings under cyclic loading

Shear walls are often used as the primary lateral load resisting elements in high‐rise buildings because of their large in‐plane stiffness and strength. It is a common practice to combine rectangular walls to form T‐shaped, I‐shaped and L‐shaped walls for functionality and esthetic reasons. Three relatively slender steel reinforced concrete (SRC) shear walls with T‐shaped cross‐sections were constructed and tested to failure under cyclic lateral loading. This research was conducted to assess the failure mechanism, hysteretic behavior, ductility and energy dissipating capacity of SRC T‐shaped walls under various axial load ratios. All the specimens exhibited a flexural mode characterized by crushing of the concrete and buckling of the steel at the free web boundary. The experimental results showed good hysteretic characteristics without pinching phenomena. The ductility coefficient varied from 2.3 to 4.1, and the deformation capability decreased with the increasing of axial load ratios. The stiffness, strength and ductility of T‐shaped walls are dependent upon the direction of the applied lateral loads. Higher stiffness and strength and lower ductility are achieved when the flange is in tension. The failure mechanism suggested that special attention should be paid to the design of the free web boundary to prevent premature failure under compression. Copyright © 2014 John Wiley & Sons, Ltd.     

基于碳纤维布和角钢复合加固损伤混凝土柱抗震试验设计研究

随着建筑物在使用年限内持续使用,某些混凝土柱由于各种原因已经受到不同形式的破坏而损伤,需要进行加固处理才能继续使用。从混凝土抗震性能的角度去研究碳纤维布和角钢结合的方式加固混凝土柱,在试验过程当中我们采用4个已经损伤的混凝土柱和梁进行模拟试验,利用控制变量的方法对碳纤维的使用量和角钢的使用量进行不同的变量控制,进行多次模拟抗震指标试验,最后绘制构建的荷载-应变图形,通过分析该图形来了解加固材料碳纤维布和角钢之间的关系。     

早龄期钢纤维混凝土抗裂性能测试与计算

采用三点弯曲切口梁和楔入劈裂紧凑拉伸两种试验模型，测试早龄期阶段钢纤维混凝土材料的抗裂性能；由试验数据计算裂纹应力强度因子和断裂能等表征断裂性能参数。通过分析试验与计算数据，发现随着龄期的增长，钢纤维混凝土的承载能力和抗裂性能都不断增大，在早于7d龄期内，钢纤维与混凝土基体之间的界面作用已经比较明显，抗裂能力明显强于同阶段的普通素混凝土。     

Seismic behavior analysis for composite structures of steel frame‐reinforced concrete infill wall

The composite structure of steel frame–reinforced concrete infill wall (CSRC) combines the advantages of steel frames and reinforced concrete shear walls. Reinforced concrete infill walls increase the lateral stiffness of steel frames and reduce seismic demands on steel frames thus providing opportunities to use partially restrained connections. In order to study seismic behavior and load transfer mechanism of CSRC, a two‐story one‐bay specimen was tested under cyclic loads. With that, the main characters such as, strength, stiffness, ductility, energy dissipation, load distribution, performance of steel frames, partially restrained connections and studs, are analyzed and evaluated. The experimental results show that the structure has adequate strength redundancy and sufficient lateral stiffness. The CSRC system has good ductility and energy dissipation capability. Partially restrained connections could enhance ductility and avoid abrupt decreases in strength and stiffness after the failure of infill walls. The composite interaction is ensured by headed studs, which have failed because of low‐cycle fatigue. Steel frames bear 80%–100% of overturning moments, and the remainder is undertaken by infill walls; steel frames and infill walls resisted 10%–20% and 80%–90% of lateral loads, respectively. Furthermore, relevant design recommendations are presented. Copyright © 2011 John Wiley & Sons, Ltd.     

Seismic performance of reinforced concrete shear wall frames considering soil–foundation–structure interaction

A practical application of ‘beam on nonlinear Winkler foundation’ approach has been utilized in this paper for a case study on seismic performance of concrete shear wall frames to assess the soil–foundation–structure interaction effects. A set of 3‐, 6‐, 10‐ and 15‐story concrete shear wall frames located on hypothetically soft, medium and hard soils were designed and modeled using the OpenSees platform. The numerical model of each frame was constructed employing the distributed and lumped plasticity elements as well as the flexure–shear interaction displacement‐based beam–column elements incorporating the soil–footing interface. Pushover analysis was performed, and the results were studied through two code‐based viewpoints: (a) force‐based design and (b) performance‐based design. A comparison was made afterwards between the frame behaviors in the fixed‐/flexible‐base conditions. The results indicate some degree of inaccuracy in the fixed‐base assumption, which is regularly applied in analysis and design practice. The study emphasizes on how the fixed‐base assumption overestimates the design of the wall element and underestimates the design of the connected moment frame. Copyright © 2012 John Wiley & Sons, Ltd.     

Shear strength estimation of reinforced concrete beam–column sub‐assemblages using multiple soft computing techniques

The aim of the present study is to propose innovative predictive models for shear capacity of reinforced concrete (RC) exterior joints in terms of multiple soft computing techniques. Existing models were evaluated and by a preliminary sensitivity analysis, seven parameters including compressive strength of concrete, product of the yield stress and the reinforcement ratio of the joint stirrups, the effective width of the joint panel, cross‐sectional column width, beam tensile longitudinal reinforcement ratio, beam compressive longitudinal reinforcement ratio, and column longitudinal reinforcement ratio were considered. Then, a large data set having the details of experimental programs on shear capacity of exterior RC beam–column joints was provided. The experimental data were utilized in developing the proposed models. After verification of the new models against available database, their efficiency compared with existing models was confirmed. Finally, a sensitivity analysis was performed in order to find the relative importance of each input parameter on the shear strength of RC joints. The results indicated that the beam reinforcement is the most important factor in shear capacity estimation of exterior RC beam–column connections.     

Strength and ductility of stiffened thin-walled hollow steel structural stub columns filled with concrete

It is generally expected that inner-welded longitudinal stiffeners can be used to improve the structural performance of thin-walled hollow steel structural stub columns filled with concrete. Thirty-six specimens, including 30 stiffened stub columns and six unstiffened ones, were tested to investigate the improvement of ductile behaviour of such stiffened composite stub columns with various methods. The involved methods include increasing stiffener height, increasing stiffener number on each tube face, using saw-shaped stiffeners, welding binding or anchor bars on stiffeners, and adding steel fibres to concrete. It has been found that adding steel fibres to concrete is the most effective method in enhancing the ductility capacity, while the construction cost and difficulty will not be increased significantly.     

Experimental study on the seismic behavior of a shear wall with concrete‐filled steel tubular frames and a corrugated steel plate

Shear walls and core tubes in shear walls constitute the core anti‐earthquake vertical systems of high‐rise buildings. This paper proposes a new type of composite shear wall with concrete‐filled steel tubular frames and corrugated steel plates. The seismic behavior of the new shear wall is studied using a cyclic loading test and damage analysis. The failure mode, load‐carrying capacity, ductility, stiffness degradation, hysteresis behavior, and energy dissipating capacity exhibited in the test are studied. The test results show that when the proposed wall is broken, the tension side of concrete‐filled steel tubes is torn. The concrete at the bottom of the wall is detached and peels off along the through cracks. The energy dissipation capacity of concrete walls is more fully utilized. The proposed wall exhibits excellent deformability, energy dissipation capacity, and the stiffness degradation was slower than that of other walls. The use of corrugated steel plate significantly improved the seismic performance while simultaneously increasing the ductility and reducing the damage. In addition, this paper modified the energy dissipation factor in the Park & Ang model based on the situation of the specimen and experiment. It can be used to evaluate the damage degree of this new type of shear wall.     

钢管混凝土柱-钢梁平面框架抗震性能的试验研究

为了探讨钢管混凝土柱-钢梁平面框架的抗震性能,本文进行了12个框架试件在恒定轴力和水平反复荷载作用下的试验研究,主要考察了柱截面形状(圆形、方形)、含钢率(圆形:α=0.06,0.103;方形:α=0.125,0.126)、柱轴压比(圆形:n=0.06~0.60;方形:n=0.04~0.60)、梁柱线刚度比(圆形:i=0.36~0.58;方形:i=0.34~0.62)等参数对其力学性能的影响。试验结果表明:钢管混凝土柱-钢梁框架滞回曲线较为饱满,强度和刚度退化不明显;柱轴压比和含钢率对框架的承载力和抗震性能影响较大,随着轴压比的增大,框架的水平极限承载力下降,位移延性和耗能能力降低,而含钢率影响规律则相反;圆形截面柱框架抗震性能整体上优于方形截面柱框架。按照《钢管混凝土结构技术规程》(DBJ13—51—2003)设计的钢管混凝土框架能够满足结构抗震设计要求。     

Study on seismic performance of a super‐tall steel–concrete hybrid structure

Many steel–concrete hybrid buildings have been built in China. The seismic performance of such hybrid system is much more complicated than that of steel structure or reinforced concrete (RC) structure. A steel–concrete hybrid frame‐tube super‐tall building structure with new type of shear walls to be built in a district of seismic intensity 8 in China was studied for its structural complexity and irregularity. Both model test and numerical simulation were applied to obtain the detailed knowledge of seismic performance for this structure. First, a 1/30 scaled model structure was tested on the shaking table under different levels of earthquakes. The failure process and mechanism of the model structure are presented here. Nonlinear time‐history analysis of the prototype structure was then conducted by using the software PERFORM‐3D. The dynamic characteristics, inter‐story drift ratios and energy dissipation conditions are introduced. On the basis of the comparison between the deformation demand and capacity of main structural components at individual performance level under different earthquake level, the seismic performance at the member level was also evaluated. Despite the structural complexity and code‐exceeding height, both experimental and analytical results indicate that the overall seismic performance of the structure meet the requirements of the Chinese design code. Copyright © 2012 John Wiley & Sons, Ltd.     

Investigation of Park–Ang damage index model for flexural behavior of reinforced concrete columns

One of the most popular damage indexes for reinforced concrete (RC) members is Park–Ang damage index model. This model has been established on the basis of experimental results of RC beams and columns with different modes of damage. It has considerable uncertainty on the basis of its authors' remarks. In this study, precision of Park–Ang model for RC columns is improved by using some experimental results from Pacific Earthquake Engineering Research information bank. In proposed model, it focused on RC columns with specific sections and collapse modes. Finally, in order to define damage index more exactly in concrete columns under seismic loadings, capability of IDARC‐2D computer program has been improved by this proposed model. Copyright © 2012 John Wiley & Sons, Ltd.     

Seismic performance of a reinforced concrete frame equipped with a double‐stage yield buckling restrained brace

In this paper, a double‐stage yield buckling restrained brace (DYB) is proposed to prevent soft story collapse in structures subjected to strong earthquakes. The DYB consists of two conventional buckling restrained braces (BRBs) with different yield forces: a large BRB and a small BRB. The deformation of the small BRB has an upper threshold value, controlled by a special mechanical mechanism. Once the force acting on the DYB exceeds the yield force of the small BRB, the small BRB yields and the deformation concentrates on the small BRB. When the deformation of the small BRB reaches the threshold value, the small BRB stops deforming. If the force of the DYB continues to increase and exceeds the yield force of the large BRB, the large BRB yields and most of the deformation takes place in the large BRB. In this way, the DYB achieves a double‐stage yield mechanism. To demonstrate the effectiveness of the DYB, a model of a six‐story reinforced concrete frame equipped with DYBs was constructed using the finite element software ABAQUS, and its seismic performance was analyzed. The double‐stage yield mechanism of the DYB was simulated by a gap element. To investigate the effect of DYBs on the seismic performance of the structure, four different models were built: an unbraced frame, frame with DYB, frame with small BRB, and frame with large BRB. The results of the pushover and time‐series analyses showed that the DYB effectively controlled the deformation pattern of the structures, and prevented weak story collapse.     

Experimental study of lateral load behavior of H‐shaped precast reinforced concrete shear walls with bolted steel connections

This paper presents an experimental study of H‐shaped precast reinforced concrete shear walls involving vertical connections under combined vertical and lateral loading. The H‐wall is composed of two prefabricated flange wall panels: one prefabricated web wall panel and vertical bolted steel connections between the flange and web panels. The assembling of the H‐wall is completely dry without any in situ casting. Three H‐wall specimens were constructed and tested to investigate the mechanical behavior and seismic performance of them. The lateral load‐bearing capacity, ductility, energy dissipation, lateral stiffness, strain in the connecting steel frame, and sliding within the bolted steel connections are presented and discussed to evaluate the effectiveness of the vertical connections. The ultimate shear‐resistance mechanism of the precast H‐wall assembly is also analyzed. The H‐wall assemblies generally possess high load‐bearing capacity, favorable ductility, and good energy‐dissipating capacity. The thickness of the steel plates in the connecting steel frame affects the lateral stiffness and the ultimate load‐bearing capacity of the H‐walls. Furthermore, the encasing steel plates for the web wall panel not only helps transfer the stress in the wall steel bars but also confines the concrete resulting in improved ductility.     

世博会主题馆预应力混凝土梁-钢骨变截面劲性柱节点设计及试验研究

为研究预应力混凝土梁-钢骨变截面劲性柱节点的破坏特征及受力性能,进行了4个模型试件的低周反复荷载试验。观察了各节点的受力过程及破坏形态,并分析了试件的荷载-位移滞回曲线、骨架曲线、承载能力和延性等力学特性。结果表明：预应力混凝土梁-钢骨变截面劲性柱节点典型破坏形态是梁端弯剪破坏,该类节点的延性与混凝土梁柱节点相似,位移延性系数为2.0,柱内钢骨可提高节点的承载能力及刚度;柱内钢骨变截面可有效改善节点的延性性能,而对承载能力没有影响;节点处混凝土的浇筑质量对节点的整体受力性能影响较大。最后对该类节点给出了设计及施工建议。试验研究成果可为预应力混凝土梁-钢骨变截面劲性柱节点工程研究及应用提供参考。     

Seismic behavior of specially shaped concrete‐filled steel tube columns with multiple cavities

To study the seismic behavior of specially shaped concrete‐filled tube (CFT) columns with multiple cavities under axial tension or axial compression, a quasistatic test of four 1/30‐scale specially shaped CFT columns with multiple cavities was conducted based on the CFT mega columns in a super‐high‐rise building. The main parameters of the 4 specimens were the direction of axial force, the direction of horizontal force, and the cross‐sectional structural form. The test was conducted twice at each level of horizontal displacement. The results shows that the compression–flexure test specimen showed lower yield damage, higher bearing capacity, and superior seismic performance relative to the tension–flexure test specimen; the specimen loaded along the short axis of the section had a lower bearing capacity and stiffness relative to the specimen loaded along the long axis; and the corner‐reinforced specimen with a round steel pipe was found to be rationally designed and properly constructed. Finally, an N–M correlation curve was generated and found to show satisfactory agreement between the fitted values and the test values.     

Experimental investigation of a self‐centering precast concrete beam‐to‐column connection with top and bottom friction energy dissipaters

The new friction material, non‐asbestos organic, and Belleville springs are applied to the friction energy dissipaters (FEDs) to improve its friction performance. The new high‐performance FEDs are placed in the top and bottom parts of the self‐centering precast concrete (SCPC) beam‐to‐column connections, which have inherently reduced residual deformation caused by posttensioned tendons, to enhance energy dissipation efficiency. Besides, the reasonable design of the connection between FEDs and backbone members makes it easy for the disassembly of all members, which significantly enhances the repair efficiency after a major earthquake. Theoretical analyses and 14 tests were performed on a full‐scale specimen, which were assembled two times, and the friction pads were replaced one time, to investigate the effects of various parameters on the performance of such FED‐SCPC beam‐to‐column connections. The influence of key design parameters on the hysteretic behaviors, such as stiffness, loss of posttensioned tendons force, self‐centering capacity, and energy dissipation capacity, has been analyzed. The test results indicate that the FED‐SCPC beam‐to‐column connections can achieve significant and reliable energy dissipation levels while maintaining self‐centering capabilities. The experimental and theoretical results can provide certain references for the seismic design and assembly of such structures.     

Seismic retrofitting of old‐type RC columns with different lap splices by NSM GFRP and steel bars

This paper describes the experimental results from flexural strengthening of old‐type concrete columns reinforced with plain bars and different lap splices constructed before the 1970s. Nine half‐scale column specimens were tested under combined constant axial and quasi‐static cyclic lateral loads. The specimens included 3 control specimens and 6 other specimens strengthened via near surface mounted technique with glass‐fiber reinforced plastic and steel bars. The effect of different longitudinal bar lap splices of columns and the type of strengthening materials were also investigated. The results indicated that the proposed strengthening method significantly increases the flexural strength and improves the seismic parameters, for example, energy dissipation and hysteresis damping. The specimens strengthened with steel bars presented higher strength, ductility, and hysteresis damping compared to those strengthened with glass‐fiber reinforced plastic bars. The formation of struts at the control specimen with hooked lap splices caused severe damages at the spliced region; if appropriate wrapping is done at the column end, these damages will be constrained. Using steel bars as near surface mounted reinforcement, utilizing epoxy resins as bonding agent, and installing fiber‐reinforced polymer wrapping at the end of column will all make a more effective strengthening method. Finally, an analytical work was presented for predicting the capacity of test specimens, and the comparison between experimental results and theoretical predictions showed a good agreement.