Experimental investigation of the influence of joint connection details between existing buildings and added new frames on failure mode of retrofitted slabs for the vertical expansion of old buildings: Part II

Dismantling entire existing buildings can be circumvented by adding additional frames to provide more residence, thus avoiding the need to reconstruct buildings. The alternatives are to construct new frames on old apartment buildings in order to avoid entirely dismantling existing buildings. The conventional wall frames for super structures added onto existing buildings are replaced by frames consisting of composite beams and steel columns to minimize beam depth and weight of the load from the added frames. This paper studied joint connection types for the rehabilitation of old buildings to withstand lateral loads. Details of the joints between newly added steel columns and existing slabs are presented in this paper. The structural behaviors of anchored joints between the new 3‐story composite frames and an existing 15‐floor building were significantly investigated through extensive experiments. Complex failure modes were identified based on the test of the wall foundation types and the anchor types connecting the base plates to existing slabs. The authors previously reported that the flexural load‐bearing capacity of slabs was the dominant load‐resisting capacity. The column–slab joint connections introduced with experimental demonstrations in this study are expected to contribute to enhancing the lateral capacity of the extended buildings.     

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.     

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

This paper proposed a precast concrete‐based dry mechanical joint for fully‐restrained moment connections which can be used to connect reinforced concrete precast columns. In the proposed connections, a pair of steel plates is provided and connected by high‐strength bolts to transfer axial loads and moments. One plate is installed at the bottom of upper columns, and another one is placed on the top of lower columns. The stiffness of the column plates is determined to enable axial loads and the moment to be transferred at joints, providing a fully‐restrained moment connection between columns. The structural behavior of the moment connections was evaluated through experimental and analytical investigations. Through extensive experimental investigations, columns jointed with plates capable of sufficient stiffness and strength demonstrated structural behavior similar to those of conventional columns. The plate deformations which fail to transfer the moment were not prevented with columns jointed by plates incapable of providing sufficient stiffness and strength. A good match in terms of the load–displacement relationship and plate deformation was also demonstrated between the finite element analysis based prediction and the test data for all specimens. The introduced connections will contribute to modular offsite construction for buildings and heavy industrial plants.     

Experimental investigation of the influence of steel joints upon the flexural capacity of precast concrete columns

In previous studies, the authors have shown that successful modular construction depends on using the correct types of joint connections. In this experimental study, steel beam–column joint connections were shown to be very efficient in facilitating the construction of modular frames while ensuring sufficient flexural moment capacity at the joints to resist lateral loads. This research also included an investigation of the behavior, the crack pattern, and the flexural moment capacity of concrete columns with hybrid composite joints by means of structural experiments on three specimens. Three column specimens were subjected to cyclic loading under displacement control using an oil jack. The influence of including steel sections at the beam–column joint upon the flexural moment capacity of the column was studied, and the use of concrete–steel hybrid composite joints was found to increase the flexural structural performance of the concrete columns. The flexural moment capacity in the maximum load limit state of a concrete column with steel joints was 43.2% greater than that of a conventional reinforced concrete column without steel joints. The steel section in the joint was found to greatly contribute to the flexural moment capacity and to the modular construction technologies.     

Structural design of high‐rise buildings using steel‐framed modules: A case study in Hong Kong

Steel‐framed modular buildings afford certain advantages, such as rapid and high‐quality construction. However, although steel‐framed modules have been adopted in several countries, most of them are limited to low‐to‐medium‐rise structures; modular high‐rise buildings are rare. This study proposes a feasible structural design solution for high‐rise buildings using a steel‐framed modular system. A 31‐story student hostel building in Hong Kong is redesigned as a steel‐framed modular building and used as a case study. The finite element models of the building are formulated, and the structural behaviors under wind and earthquake load scenarios are compared. Moreover, the structural design process used for the 31‐story building is applied to design a hypothetical 40‐story modular building to further examine the proposed design solution. The numerical analysis results indicate that the roof lateral displacements and interstory drift ratios of the redesigned modular building are within the allowable limits of design codes; moreover, the modular connections behave elastically under the most adverse loading scenarios. Accordingly, the proposed solution can be used to design steel‐framed modular buildings of up to 40 stories, while complying with relevant wind and seismic codes.     

Composite steel and concrete structural systems for seismic engineering

Research within the United States on seismic engineering of buildings using composite steel/concrete structural systems has increased dramatically in the past decade. This paper summarizes recent research on a number of these composite lateral resistance systems, including unbraced moment frames consisting of steel girders with concrete-filled steel tube (CFT) or steel reinforced concrete (SRC) columns; braced frames having concrete-filled steel tube columns; and a variety of composite and hybrid wall systems. The benefits of these structural systems relative to more common systems include their performance characteristics when subjected to service or ultimate loads, and their economy with respect both to material and construction. In addition, more in-depth research results will be presented on one of these composite systems, consisting of partially-restrained steel frames with composite reinforced concrete infill walls. The paper concludes with a summary of probable future design provisions for these composite systems.     

带构造柱双排孔混凝土空心砌块墙抗震性能试验研究

双排孔混凝土小型空心砌块中间孔洞较小无法设置芯柱,故设置构造柱是提高这种砌块建筑水平抗侧力性能的主要措施。为了研究这种结构体系的抗震性能,本文对7个设置构造柱双排孔混凝土空心砌块承重墙原型试件进行了低周反复荷载试验。得到了其承载力、延性和耗能等实测数据,并分析了墙片单元X形裂缝的破坏特征。试验及分析表明,双排孔混凝土小型空心砌块承重墙片在采用了约束构造柱等措施后,约束构造柱对墙体可起到有效约束作用,使破碎的墙体不倒塌,具有良好的抗震性能。     

型钢混凝土异形柱抗震性能试验研究

对17个型钢混凝土(SRC)异形柱试件采用“建研式”加载装置进行低周反复荷载试验,观察了不同配钢形式的SRC异形柱的受力过程和破坏形态;分析了SRC异形柱的破坏特点,荷载-位移滞回曲线及骨架曲线、承载力、位移延性、刚度退化和耗能能力等力学性能。试验研究结果表明:SRC异形柱的主要破坏形态是剪切斜压破坏和弯曲型破坏,破坏主要发生在与加载方向平行的柱肢,滞回曲线对称、饱满,试件延性好,极限侧移角大,具有良好的抗震能力,因此,可以推广应用于高抗震设防烈度区的建筑以及高层建筑中。     

装配式钢管混凝土组合框架的抗震性能试验研究

圆形或方形钢管混凝土柱与钢梁通过单边高强螺栓和适宜端板连接组成框架,通过钢筋桁架混凝土组合楼板形成了新型装配式组合框架。为了解装配式钢管混凝土组合框架在地震作用下的抗震性能和受力机理,进行了2榀两层单跨钢管混凝土柱与钢-混凝土组合梁通过单边高强度螺栓和平齐或外伸端板连接形成的组合框架的水平低周反复荷载试验,研究了柱截面形式和端板连接类型对组合框架破坏形式和抗震性能的影响。详细地观察了此类组合框架在水平低周反复荷载作用下的受力全过程和楼板裂缝发展规律,得到了此类结构的滞回曲线、骨架曲线、刚度退化规律、延性、耗能能力等抗震性能指标。试验结果表明,单边螺栓端板连接装配式钢管混凝土组合框架结构具有良好的滞回性能和耗能能力,延性系数μ为2.13~4.28,能量耗散系数E为0.652~0.90。在柱截面含钢率相同条件下,圆钢管混凝土组合框架的承载力小于方钢管混凝土组合框架,其延性、耗能性能优于方钢管混凝土组合框架。研究成果将为我国装配式钢管混凝土组合框架设计理论与应用提供科学依据。     

抗震工程中的钢和混凝土组合结构体系分析

过去10年里,美国国内关于钢和混凝土组合体系建筑抗震工程的研究有显著的增多。对最近一系列组合横向阻力系统的研究进行了概述,包括由钢梁和混凝土填充的钢管组成的无支撑框架,带有混凝土填充钢管柱的支撑框架,型钢混凝土柱以及一系列变化的组合混杂墙系统。相对于很多一般的系统,这些结构体系的优点包括它们在承受正常使用或极限荷载时的性能特征,以及材料与结构的经济性。此外,介绍其中一种混合系统深入研究的成果,包括部分约束的带有加强混凝土填充墙的钢框架。总结出这些组合体系将来设计条款的概要。     

Testing of self-consolidating concrete-filled double skin tubular stub columns exposed to fire

A concrete-filled double skin tube (CFDST) is an innovative steel and concrete composite construction with the potential to be used as columns in high-rise buildings. Self-consolidating concrete (SCC) can offer convenience for construction and ensure the construction quality of CFDST columns. There is very limited knowledge about the fire performance of CFDST columns, which is a key issue in the application to high-rise buildings. This paper reports an experimental investigation into the fire behaviour of CFDST stub columns filled with SCC and fibre reinforced SCC. The study aims to obtain thermal and structural responses of the stub columns through standard fire testing. Details are given in terms of the failure mode, temperature distribution, critical or limiting temperature and fire resistance. It was found that the added fibre does not affect the temperature distribution whereas the increased concrete thickness and outer tube perimeter reduces the temperature in CFDST specimens. The added steel fibre increases the fire resistance of CFDST stub columns especially for load levels less than 0.6. The critical or limiting temperature for CFDST sections was found to be higher than for CFST (concrete-filled steel tube) or unfilled tubes.     

抗震工程中的钢-混凝土组合结构体系分析

过去10年里,美国关于钢-混凝土组合结构体系抗震性能的研究显著增多。介绍了最近一系列组合横向抗力体系的研究成果,包括由钢梁和钢管混凝土柱或型钢混凝土柱组成的无支撑框架,带钢管混凝土柱的支撑框架及各种组合、混杂墙结构。相比于一般体系,该体系在正常使用或极限状态下的性能及材料与结构的经济性等方面都有许多优点。此外,介绍由带钢筋混凝土填充墙的部分约束钢框架组成的组合体系的深入研究成果。最后,总结了未来对这些组合体系设计的可能规定。     

带PEC柱的钢板剪力墙结构抗震性能试验研究

为了解决薄钢板剪力墙结构中框架柱易发生破坏而失效的问题,将强度高、刚度大的PEC柱引入薄钢板剪力墙结构,作为竖向边缘构件形成PEC-SPSW结构,分别对1榀带H形钢柱、2榀带PEC柱的钢板剪力墙结构,进行了低周往复荷载作用下的抗震性能试验研究。通过分析该结构的承载力、初始刚度、耗能能力、应力分布及破坏模式,得到了带PEC柱的钢板剪力墙结构具有更好的抗侧刚度、承载力和耗能性能。PEC柱构件对薄钢板有更好的锚固约束作用,从而使得薄钢板充分发挥屈曲后强度作用,带PEC柱的钢板剪力墙结构有更好的发展前景。     

Seismic performance of Y‐type eccentrically braced frames combined with high‐strength steel based on performance‐based seismic design

In the Y‐type eccentrically braced frame structures, the links as fuses are generally located outside the beams; the links can be easily repairable or replaceable after earthquake without obvious damage in the slab and beam. The non‐dissipative member (beams, braces, and columns) in the Y‐type eccentrically braced frames are overestimated designed to ensure adequate plastic deformation of links with dissipating sufficient energy. However, the traditionally code design not only wastes steel but also limits the application of eccentrically braced frames. In this paper, Y‐type eccentrically braced steel frames with high‐strength steel is proposed; links and braces are fabricated with Q345 steel (the nominal yield stress is 345 MPa); the beams and columns are fabricated with high‐strength steel. The usage of high‐strength steel effectively decreases the cross sections of structural members as well as reduces the construction cost. The performance‐based seismic design of eccentrically braced frames was proposed to achieve the ideal failure mode and the same objective. Based on this method, four groups Y‐type eccentrically braced frames of 5‐story, 10‐story, 15‐story, and 20‐story models with ideal failure modes were designed, and each group includes Y‐type eccentrically braced frames with ordinary steel and Y‐type eccentrically braced frames with high‐strength steel. Nonlinear pushover and nonlinear dynamic analyses were performed on all prototypes, and the near‐fault and far‐fault ground motions are considered. The bearing capacity, lateral stiffness, story drift, link rotations, and failure modes were compared. The results indicated that Y‐type eccentrically braced frames with high‐strength steel have a similar bearing capacity to ordinary steel; however, the lateral stiffness of Y‐type eccentrically braced frames with high‐strength steel is smaller. Similar failure modes and story drift distribution of the prototype structures designed using the performance‐based seismic design method are performed under rare earthquake conditions.     

Performance‐based seismic rehabilitation of existing steel eccentric braced buildings in near fault ground motions

The devastating effects observed in the recent earthquakes, in terms of loss of lives as well as immediate and long‐term economic losses, have prompted the need to provide documents concerning the assessment and improvement of the structural performance of existing buildings at the time of an earthquake. In this regard, performance engineering is defined as performance‐based seismic design and rehabilitation. There are many reasons for rehabilitation of existing buildings. Changing the building's usage is one of the most common reasons. In the present study, the residential steel buildings were subject to performance‐based rehabilitation, converting to educational use. Several steel frames with dual lateral‐resistant systems (MRF–EBF) and different numbers of stories were initially designed as residential buildings. The frames were rehabilitated according to the current seismic rehabilitation codes and regulations. Cover plates were used to strengthen structural elements. Variations in structural responses were evaluated before and after retrofitting by the use of nonlinear analysis. Moreover, the performance of rehabilitated structures was evaluated, considering the gross features observed in near‐field records. Copyright © 2013 John Wiley & Sons, Ltd.     

Continuous transfer beams supporting in-plane loaded shear walls in tall buildings

The failure mechanism and structural behavior of transfer beams supporting in-plane loaded shear walls have received added emphasis owing to their importance in connection with tall building construction. This paper presents an analysis of and investigation of the structural behavior of two-span transfer beam-shear wall systems in tall buildings. The interaction between the transfer girders and the shear wall has been investigated considering interior and exterior column interaction effects. The upper structural form has a significant effect on the failure mechanism of the transfer girders, which can act as full tension members or behave as ordinary flexural beams. Stress distributions in the shear wall interactive zone are presented. The relevant parameters that significantly influence the force transfer mechanism and structural behavior, such as the span/depth ratio of the transfer beam, the span of the shear wall and the stiffness of the support columns, are highlighted. The present paper provides a very useful reference for the design of continuous transfer girders supporting in-plane loaded shear walls in tall buildings.     

外挂复合墙板半刚性钢管混凝土框架抗震试验研究

为了研究在地震作用下外挂复合墙板装配式钢结构的抗震性能,本文进行了4榀外挂复 合墙板半刚性钢管混凝土框架试件和1榀半刚性钢管混凝土框架试件的水平低周反复荷载试验。 研究参数为墙板的混凝土类型、墙连方式、斜撑设置和是否设置墙板。研究了地震作用下墙板 与框架的共同工作性能和破坏模式,分析了结构的滞回曲线、骨架曲线、强度和刚度退化规律 、耗能能力等。结合现有规范评价了结构的延性。试验结果表明,采用螺栓连接方式外挂复合 墙板的半刚性钢管混凝土框架试件具有良好的滞回性能、耗能能力和延性,可以安全可靠地确 保复合墙板与组合框架在地震作用下共同工作;位移延性系数μ=2.53~3.81,弹性极位移角 θy=(3.33~5.03)［θe］,弹塑性极限位移角θf=(2.35~2.55)［θp］;等效黏滞阻尼系数 ξe=0.147~0.182,能量耗散系数E=0.973~1.145;复合墙板破坏主要发生在墙板预埋件附近, 整体性能优于传统墙体。研究成果将为我国装配式钢结构设计理论与应用提供科学依据。     

砖混教学楼横墙不同构造条件下的抗震性能试验研究

为研究圈梁和构造柱的布置方式对砖混结构教学楼横墙抗震性能的影响,按照1/2的缩尺比例设计制作了5片横墙试件,试件类型包括无构造柱横墙体、两端设置构造柱的普通墙体试件以及在墙体中加设构造柱和圈梁形成的组合墙体等,采用拟静力试验对各试件的破坏特点、变形能力和耗能能力等进行了研究。结果表明,圈梁和构造柱的布置方式决定了横墙的抗震性能,按照现行GB 50011—2010《建筑抗震设计规范》在横墙两端设置构造柱,同时确保墙体与基础梁间不发生剪切滑移破坏,则横墙表现出较好抗震性能,墙体中加设1根构造柱或同时再加设1根圈梁形成的组合墙体的抗震性能并没有得到有效改善,但加设圈梁和构造柱的墙体试件在极限变形后破坏墙块的变形受到中间圈梁的约束,墙体具有较好的后期整体性。     

装配式模块建筑组合钢柱耐火性能试验研究

采用耐火试验炉对装配式模块建筑四柱组合的钢结构构件开展不同防火保护条件下的试验研究,分析了模块建筑组合钢柱在火灾下的试验现象、升温曲线、变形特点及破坏形态,获取了模块建筑组合钢柱的耐火极限,以此对模块建筑组合钢柱的防火保护构造提出了设计建议。结果表明：8 mm厚的组合钢柱构件,在双层20 mm高性能防火石膏板的保护下,耐火极限不低于2.50 h,满足二级耐火等级建筑要求;在双层12 mm厚纤维增强硅酸板和60 mm厚岩棉的保护下,耐火极限不低于3.00 h,满足一级耐火等级建筑要求;在三层高性能防火石膏板（15 mm+20 mm+20 mm）的保护下,耐火极限不低于4.00 h。     

Monotonic and cyclic loading tests for cold-formed steel wall frames sheathed with calcium silicate board

This research is concentrated on the structural strength and behavior of cold-formed steel wall frame sheathed with calcium silicate board under shear load. Test specimens with two different thicknesses of sheathing were assembled, 9 mm and 12 mm, with one-side or two-side of attachment. Monotonic shear and cyclic loading tests are conducted on wall specimens utilizing two C sections connected back-to-back to be as chord studs and calcium silicate board sheathing on the exterior. Based on the test results, detailed discussions on the strength, stiffness, energy absorption, ductility ratio, and failure mode of cold-formed steel wall specimens are given. It is noted that the failure mostly occurred at the bottom track of wall specimens due to the large deformation or tearing failure of track. The wall strength is not affected by the change of sheathing's thickness significantly, but wall frames attached with two-side calcium silicate board sheathing provide higher resisting strength and stiffness than those attached with one-side sheathing. In this study, test results are also used to compare with the previous study that single chord stud was used in the assembly of wall frame. In addition, the suggested response modification factor of the wall sheathed with calcium silicate board is proposed for design purpose.