基于屈服点谱法的中心支撑钢框架抗震性态评估

屈服点谱(Yield Point Spectra,YPS)是以位移-加速度表述的反应谱形式。YPS可以用于对现有结构进行抗震评估,确定结构在给定地震作用下的峰值位移和延性。本文按照我国设计规范分别设计了6层、9层、12层3个人字形中心支撑钢框架结构,利用YPS对3个结构进行非线性静力分析,得到结构在设防地震和罕遇地震下的峰值位移和层间位移角,并与SAP2000动力时程分析得到的结果进行对比,评估人字形中心支撑钢框架在设防地震和罕遇地震下的抗震性态,评价了YPS方法用于中心支撑钢框架抗震性态评估的可靠性。     

Progressive collapse analysis of seismically designed steel braced frames

The progressive collapse resistance of seismically designed steel braced frames is investigated using validated computational simulation models. Two types of braced systems are considered: namely, special concentrically braced frames and eccentrically braced frames. The study is conducted on previously designed 10-story prototype buildings by applying the alternate path method. In this methodology, critical columns and adjacent braces, if present, are instantaneously removed from an analysis model and the ability of the model to successfully absorb member loss is investigated. Member removal in this manner is intended to represent a situation where an extreme event or abnormal load destroys the member. The simulation results show that while both systems benefit from placement of the seismically designed frames on the perimeter of the building, the eccentrically braced frame is less vulnerable to progressive collapse than the special concentrically braced frame. Improvement in behavior is due to improved system and member layouts in the former compared to the latter rather than the use of more stringent seismic detailing.     

支撑形式对钢框架结构抗震性能影响

钢结构框架类型,按其抗侧力体系可以分为:纯框架(UBF)、中心支撑框架(CBF)和偏心支撑框架(EBF)。纯框架具有较好的延性,刚度较小,往往满足了抗震变形要求;支撑框架刚度较大,具有两道纯抗震防线,适应于抗震设防较高的地区。通过有限元软件ANSYS对6层框架进行动力分析,比较这三种框架的抗震性能。由分析可知,支撑框架能较好地控制结构变形。     

Ductility reduction factor and collapse mechanism evaluation of a new steel knee braced frame

In this study, the suitability of a new structural system called the knee braced frames (KBFs) is investigated for seismic resistant steel structures. In these structural systems, ends of beams are connected to columns by hinges (simple connection) instead of rigid connections, and ends of knee braced elements are connected to columns and beams by hinges as well. In the present paper, in addition to a comparison between elastic behaviour and elastic fundamental natural period, the ductility reduction factor and the type of collapse mechanism in steel KBFs and steel moment resisting frames (MRFs) are compared. The study revealed that the stiffness of steel buildings can be increased considerably by applying knee braced elements and the effects of knee braced elements are highly dependent on knee braced configuration. By applying the pushover analysis, it was observed that the type of collapse mechanism of KBFs is very similar to the mechanism of MRFs. Furthermore in most cases, the ductility reduction factor, R_μ, obtained from steel KBFs is greater than the ductility reduction factor obtained for steel MRFs. Based on the similarity between type of collapse mechanism and the proximity of ductility reduction coefficients of the KBFs and MRFs systems, it can be concluded that the new steel knee braced frame systems can be categorised as steel MRFs with rigid connections.     

Comparative study of special and ordinary braced frames

The collapse probability of ductile and non‐ductile concentrically braced frames was investigated using nonlinear dynamic response analysis. Two buildings with three and nine stories located in Boston and Los Angeles, respectively, were designed and subjected to ground motions from the areas. In Boston area, three‐story and nine‐story buildings were designed as ordinary concentrically braced frame with response modification reduction factor R equal to 3 1/4 to be considered as non‐ductile structural systems; comparatively, in Los Angeles area, three‐story and nine‐story buildings were designed as special concentrically braced frame with response modification reduction factor R equal to 6 to be considered as ductile structural systems. In order to evaluate the performance of ductile and non‐ductile concentrically braced frames in moderate and severe seismic regions, ATC‐63 would be used as reference to assess the seismic behaviors. Evaluation approach recommended by ATC‐63 was adopted, and hundreds of nonlinear dynamic analyses were performed. Through alternating the scale factors of designated ground motions, median of structural collapse intensity was presented for each structure. By observing the results of statistical performance assessment, the seismic performance of the systems was evaluated, and some observations are made based on the study. Copyright © 2012 John Wiley & Sons, Ltd.     

大型火电厂钢结构主厂房铰接中心支撑框架体系的振动台试验研究

为获得铰接中心支撑框架结构体系的抗震性能,以位于抗震设防烈度8度区的某大型火电厂钢结构主厂房横向最不利一榀的煤仓间部分为原型,按1∶12缩尺比例设计制作了试验模型,并对其进行了14种地震工况下的模拟地震作用振动台试验。得到了模型结构的动力特性、阻尼比及其在8度多遇、基本和罕遇烈度下的加速度和位移响应等。结果表明:8度多遇地震作用前后结构第1阶频率为4.59Hz,8度罕遇地震作用后,第1阶频率减小为4.40Hz,但梁柱仍然完好,仅有个别支撑和节点板出现了微小的平面外变形。依据试验与有限元分析结果,推算出试验原型结构在三种地震(E l Centro、CholamShandon、人工地震)的多遇烈度以及人工地震的罕遇烈度下,层间位移角均满足我国现行抗震规范要求。该体系在高烈度区也可具有良好的抗震性能。     

An investigation on the accuracy of pushover analysis for estimating the seismic deformation of braced steel frames

This paper investigates the potentialities of the pushover analysis to estimate the seismic deformation demands of concentrically braced steel frames. Reliability of the pushover analysis has been verified by conducting nonlinear dynamic analysis on 5, 10 and 15 story frames subjected to 15 synthetic earthquake records representing a design spectrum. It is shown that pushover analysis with predetermined lateral load pattern provides questionable estimates of inter-story drift. To overcome this inadequacy, a simplified analytical model for seismic response prediction of concentrically braced frames is proposed. In this approach, a multistory frame is reduced to an equivalent shear-building model by performing a pushover analysis. A conventional shear-building model has been modified by introducing supplementary springs to account for flexural displacements in addition to shear displacements. It is shown that modified shear-building models have a better estimation of the nonlinear dynamic response of real framed structures compared to nonlinear static procedures.     

耗能梁段长度对K形偏心支撑钢框架抗震性能的影响

分析了K形偏心支撑钢框架中耗能梁段的受力特性,利用非线性有限元程序探讨了耗能梁段长度对K形偏心支撑钢框架刚度、延性及耗能性能的影响,提出了初步设计时耗能梁段长度的取值范围。     

Moment frames – concentrically braced frames dual systems: analysis of different design criteria

In this paper, a design methodology based on the theory of plastic mechanism control (TPMC) is presented for dual systems combined by moment resisting frames and concentrically braced frames (MRF–CBF dual systems). The study is focused on the design of structures failing in global mode, i.e. whose collapse mechanism is characterised by the yielding of all the tensile diagonals, the buckling of the compressed ones, and the development of plastic hinges at all the beam ends and at the base of first-storey columns. The results of push-over analyses and nonlinear dynamic analyses carried out with reference to MRF–CBF dual systems designed according to the proposed procedure are compared with those obtained with reference to the same structural scheme designed according to Eurocode 8. The advantages obtained in terms of seismic performances are outlined and also economic issues are investigated pointing out the convenience of seismic design based on TPMC.     

Evaluating response modification factors of concentrically braced steel frames

Response modification factor is one of the seismic design parameters to consider nonlinear performance of building structures during strong earthquake. Relying on this, many seismic design codes led to reduce loads. The present paper tries to evaluate the response modification factors of conventional concentric braced frames (CBFs) as well as buckling restrained braced frames (BRBFs). Since, the response modification factor depends on ductility and overstrength, the static nonlinear analysis has been performed on building models including single and double bracing bays, multi-floors and different brace configurations (chevron V, invert V and X bracing). The CBFs and BRBFs values for factors such as ductility, overstrength, force reduction due to ductility and response modification have been assessed for all the buildings. The results showed that the response modification factors for BRBFs were higher than the CBFs one. It was found that the number of bracing bays and height of buildings have had greater effect on the response modification factors.     

耗能梁段长度对K形偏心支撑钢框架抗震性能的影响

分析了K形偏心支撑钢框架中耗能梁段的受力特性,利用非线性有限元程序探讨了耗能梁段长度对K形偏心支撑钢框架刚度、延性及耗能性能的影响,提出了初步设计时耗能梁段长度的取值范围.     

Stochastic optimisation of buckling restrained braced frames under seismic loading

A stochastic optimisation procedure is proposed for the design of low- and mid-rise buckling restrained braced frames subject to seismic loading. The seismic excitation is represented as a zero-mean nonstationary filtered white noise. The Bouc–Wen model is chosen to represent the hysteretic behaviour of the buckling restrained braces. The equivalent linearisation method is employed to determine the second-order statistics of structural responses from the non-linear system. Three seismic intensity levels are considered in this study, which are associated to earthquakes with different probability of occurrence during the building’s lifecycle. It was observed that the optimal design that minimises the maximum ductility demand produces a more uniform distribution of energy dissipation and avoids soft-storey mechanisms; therefore, this design objective is considered to be a more reasonable optimisation objective for the design of buckling restrained braced frames. For higher rise structures, buckling restrained braces may experience over-dimensioning in the top stories, which means that dissipation will not occur. Thus, an upper bound constraint for the stiffness design of the buckling restrained braces is taken into account.     

Seismic behavior of coupled shear wall structures with various concrete and steel coupling beams

A novel 2‐level yielding steel coupling beam (TYSCB) has been developed to enhance the seismic performance of coupled shear wall systems. The TYSCB consists of a shear‐yielding beam designed to yield first under minor earthquakes and a bend‐yielding beam designed to yield under severe earthquakes. A comparison of seismic behavior of 4 20‐storey coupled shear wall structures with reinforced concrete coupling beams, complete steel coupling beams, fuse steel coupling beams, and TYSCB is presented. The dimensions and force‐displacement curves of these coupling beams are first designed. Nonlinear dynamic analyses on these structures are carried out under minor and severe earthquakes. The seismic behavior of these models is studied by comparing their storey shear forces, storey drift ratios and ductility demands. The results show that the base shear and storey drift of the structure with TYSCB under both minor and severe earthquakes are less than those of structures with concrete coupling beams and complete steel coupling beams. Furthermore, the ductility demand of coupled shear walls with TYSCB subjected to severe earthquakes can be greatly released compared with those using fuse steel coupling beams. This indicates that the proposed TYSCB has a better balance between ductility demand and energy dissipation, compared to traditional steel coupling beams.     

Cyclic behavior studies on I-section inverted V-braces and their gusset plate connections

Inverted V-braces and their central gusset plate connections are popular patterns of brace arrangements for special concentrically braced frames (SCBF). To improve the understanding of their seismic performances and promote their applications in seismic designs, the hysteretic behavior of nine I-section inverted V-braces and their gusset plate connections subject to inelastic cyclic loading is examined through experiments and analytical simulations. It is found that the clearance at the brace end on the gusset plate, the locations of the intersection point of bracing members, and the ratio of the free edge length to the gusset plate thickness are the key parameters. The loading capacities of braced frames show no decrease before the brace low-cycle fatigue fracture, but a longer plateau at a lower load level exists in the hysteretic loops. Although specimens with a linear clearance exhibit better seismic behaviors, a negative clearance is also acceptable as long as the gusset plate does not fracture prior to the braces. A brace intersection point with moderate eccentricity is preferable for its better behavior and its economical dimension of the gusset plate, but the brace point location in the gusset plate could induce out-of-plane deformations in the gusset plate and cause the system ductility to deteriorate. Based upon test results, a suggested limitation of the ratio of the free edge length to thickness for the gusset plates is presented.     

Cyclic flexural analysis and behavior of beam-column connections with gusset plates

This research investigates the cyclic flexural behavior of double-angle concentrically braced frame beam-column connections using three-dimensional nonlinear finite element analysis. Prior experimental research demonstrated that such connections possess appreciable flexural stiffness, strength, and ductility. The reserve capacity provided by these connections plays a significant role in the seismic behavior of low-ductility concentrically braced frames, so knowledge about the impact of connection parameters on local limit states and global connection performance is needed for employing reserve capacity to design and assess concentrically braced frames. Finite element models were developed and validated against prior experiments with focus on the limit states of failure of the fillet weld between the gusset plate and beam, low-cycle fatigue fracture of the steel angles joining the beam and gusset plate to the column, and bolt fracture. The models were used to evaluate the flexural stiffness, strength, and ductility of braced frame connections with primary attention on the effects of beam depth, angle thickness, and a supplemental seat angle. The finite element analysis demonstrated that increasing beam depth and angle thickness and adding a supplemental seat angle all increased the stiffness and strength of the connection while maintaining deformation capacity. A procedure to estimate the flexural behavior of beam-column connections with gusset plates was developed based on the results of the numerical simulations.     

单斜杆型偏心支撑钢框架的地震反应分析

偏心支撑结构弹性阶段刚度大,塑性阶段耗能能力强,是适用于高烈度地震区的一种有效的抗侧力结构体系。采用梁单元与壳单元相结合的非线性有限元模型,对单斜杆型偏心支撑钢框架进行弹塑性时程分析,研究耗能梁段的长度、腹板高厚比和加劲肋间距的变化对单斜杆型偏心支撑钢框架结构抗震性能的影响,提出了相应的抗震设计建议。     

Y型偏心支撑钢框架在循环荷载作用下的滞回性能分析

Y型偏心支撑钢框架是一种偏心抗震耗能的结构形式。采用曲壳单元和梁单元相结合的非线性有限元分析模型,自编计算程序,分析了Y型偏心支撑钢框架在循环荷载作用下的滞回性能,提出了相应的抗震设计对策和建议。     

长耗能梁-偏心支撑机制对中心支撑钢框架结构抗震性能的影响

为研究地震作用下人字形中心支撑钢框架结构因支撑的部分失效导致的长耗能梁-偏心支撑机制对结构抗震性能的影响,基于ABAQUS建立了6层人字形中心支撑钢框架结构数值模型,开展了增量动力分析与易损性分析,对比了考虑与不考虑长耗能梁-偏心支撑机制时结构抗倒塌性能的差异,分析了结构的损伤演化过程。结果表明:长耗能梁-偏心机制改变了结构的失效过程,抑制了薄弱层的产生与发展,对结构抗震性能具有显著影响,算例结构的倒塌富余度提高20%以上; 梁的抗弯刚度对长耗能梁-偏心支撑机制具有一定影响,较大的刚度将不利于该机制的形成,降低了结构的抗倒塌能力; 在人字形中心支撑钢框架结构体系的设计与分析中,宜考虑长耗能梁-偏心支撑机制,否则将低估结构的抗倒塌性能。     

K型偏心支撑钢框架耗能梁段长度探讨

通过对具有不同耗能梁段长度的K型偏心支撑钢框架的滞回性能与耗能梁段的耗能性能进行非线性有限元分析结果表明:随着耗能梁段长度的增加,K型偏心支撑钢框架的强度、刚度、延性和耗能性能均产生了不同程度的退化现象;耗能梁段越短,其塑性变形越大,由此而导致耗能梁段过早塑性破坏的可能性也就越大,而耗能梁段过长则抗震性能较差。最后,根据有限元模拟结果对耗能梁段的长度提出了设计建议。     

Experimental and numerical investigation on full-scale tension-only concentrically braced steel beam-through frames

This paper presents an experimental investigation on two full-scale tension-only concentrically braced beam-through frames (TOCBBTFs) with through beam bolted connections. This type of TOCBBTF system features cold-formed square-tube section columns connected to H-section through beams by bolted end plate. It is commonly used in low-rise prefabricated buildings. Two two-story, four-span by one-span TOCBBTFs subjected to design vertical load were cyclically loaded horizontally to examine the seismic behavior. Stable behavior was observed up to a story drift angle of 1/10. The cyclic behavior was characterized by a linear response, followed by a slip range and a significant hardening response. Deteriorating pinched hysteresis was observed due to the occurrence of cyclic brace compression buckling and tension yielding. The structural damage evolution, ductility, stiffness and shear force distribution of the TOCBBTFs were investigated. Moreover, the finite element software ABAQUS was used to investigate the behavior of TOCBBTF by nonlinear analysis. Semi-rigid analysis produced the most reasonable prediction including initial lateral stiffness and peak story shear. The calibrated numerical models can be employed to launch further studies for this structural system.