高强度耐火钢高温下力学性能试验研究

为研究高强耐火钢在高温下的力学性能,通过国产Q345FR、Q420FR、Q460FR耐火钢的高温下稳态拉伸试验和热膨胀变形试验,得到了20~800℃下各等级耐火钢的破坏模式、应力-应变关系曲线、力学性能参数及热膨胀系数,并与普通结构钢高温性能以及欧洲、中国的抗火设计规范的相关规定进行了对比。研究结果表明：在温度低于350~400℃时,国产高强耐火钢屈服强度、抗拉强度高于常温的,当温度超过400℃后,屈服强度、抗拉强度开始快速下降;欧洲规范EC3中给出的高温下普通结构钢的弹性模量、强度计算公式不适用于高强度耐火钢;温度低于450℃时,耐火钢试验值与GB 51249—2017《建筑钢结构防火技术规范》中普通钢取值更吻合;温度高于450℃时,耐火钢试验值与规范GB 51249—2017中耐火钢取值更吻合。针对Q345FR、Q420FR、Q460FR高强耐火钢,提出了高温下弹性模量、屈服强度、抗拉强度变化系数拟合公式,可用于耐火钢结构抗火设计。     

马钢耐火钢高温下材料性能试验研究

为了得到高温下耐火钢的材料特性,对马钢集团开发的耐火钢在高温下的力学性能进行了试验研究。通过高温下的恒温加载拉伸试验,得到不同温度下耐火钢的屈服强度、极限强度、延伸率、面缩率和应力-应变关系,并测定高温下耐火钢的热膨胀系数,采用悬丝耦合共振法测定高温下耐火钢的初始弹性模量。试验表明,马钢耐火钢在600℃时的屈服强度大于常温下的2/3,弹性模量大于常温下的3/4。通过对试验结果的分析,拟合得到耐火钢的各力学指标参数随温度变化的计算公式,这些公式可用于耐火钢结构抗火性能的分析与设计。     

高温下再生混凝土梁受剪性能试验研究

对9根不同再生骨料取代率的再生混凝土梁试件进行了常温和标准升温条件下的受剪试验,研究再生粗骨料取代率和初始荷载比等对试件的破坏特征、耐火极限、温度场分布和变形性能等的影响。利用ABAQUS有限元分析软件分别进行试件的温度场分析和顺序热-应力耦合全过程分析,并提出高温下再生混凝土梁受剪承载力理论计算方法和设计计算式。研究结果表明:高温下再生混凝土梁的剪切破坏特征与普通混凝土梁相似,但再生骨料取代率越大,火灾试验后试件表面混凝土的剥落程度越明显;试件的耐火极限随再生粗骨料取代率的增大而提高,随初始荷载比的增大而降低,再生混凝土梁的耐火极限受初始荷载比的影响比普通混凝土梁低;再生粗骨料取代率越大,相同时刻试件内部测点的温度越低,箍筋温度也越低,再生混凝土梁比普通混凝土梁具有更好的耐火性能;在火灾试验末期,随着再生粗骨料取代率的增加,试件的变形增长速率逐渐减小,说明高温下再生混凝土梁斜截面破坏时的延性比普通混凝土梁好;有限元分析结果与试验结果吻合较好;提出的高温下再生混凝土梁受剪承载力理论计算方法和设计计算式均具有可行性,能够分别满足试验和工程设计的要求。     

高温下高强度螺栓20MnTiB钢的材料性能试验研究

对我国10.9级高强度螺栓常用的20MnTiB钢材进行了高温下的材料性能试验.试验得到的数据有应力-应变关系曲线、屈服强度、极限强度、弹性模量、延伸率和热膨胀系数.根据试验结果得到了可用于理论分析的20MnTiB钢高温材性模型,并将之与其他国家推荐的高温钢材模型进行了比较.本文的研究成果为钢结构高强度螺栓连接的抗火性能分析与抗火设计提供了基础.     

足尺钢框架结构真实火灾下耐火性能试验研究

为分析真实火灾下整体钢框架结构的耐火性能，设计了一个平面尺寸为6 m×6 m、单层层高为3 m的两跨两层钢框架足尺结构，并进行三种火灾工况下的真实火灾试验，研究了住宅火灾、仓库火灾及无防护火灾条件下的试验现象、实际温度场和力学响应。结果表明：真实火灾下钢框架的升温曲线与标准升温曲线有较大差别；受火房间的空气温度沿竖直方向呈现不均匀分布，沿水平方向温度趋于相同；防火保护使构件表面温度滞后于火场温度，且表面温度峰值和峰值后的下降速率均小于无防火保护构件的；火荷载密度增大及防火保护的缺失都将增加钢梁轴向的温度差，但不影响沿钢梁和钢柱截面方向以及钢柱轴向的温度梯度变化规律；钢梁和混凝土板相较钢柱具有更高的温度；钢框架结构设计应充分考虑防火保护，且可适当考虑墙体对建筑抗火性能的有利作用。     

高强度钢材螺栓连接抗剪性能试验研究

近年来高强度钢材在工程中得到了逐步推广和应用,尤其是Q460强度等级的高强度钢材。但是目前各国规范都尚未对高强度钢材螺栓连接设计方法做出具体规定,仍沿用普通强度钢材的设计方法。因此,需对端距、边距和螺栓间距等几何构造对高强度钢材螺栓抗剪连接性能的影响进行深入的试验研究。针对10,12 mm厚的Q460强度等级的高强度钢材进行螺栓抗剪连接试验,通过改变两个10.9级M27高强度螺栓的几何布置,研究不同端距、边距和螺栓间距情况下,高强度钢材的承压性能的变化情况。由试验可以观察到螺栓抗剪连接的3种不同的破坏模式:端部撕裂、孔壁拉长和板净截面拉断。同时还将试验得到的极限承载力与欧洲和美国钢结构设计规范设计值进行比较。结果发现,现有规范并不能很好地预测高强度钢材螺栓抗剪连接的破坏模式和极限强度,建议更深入地进行参数分析以完善规范设计方法。     

高温后型钢再生混凝土梁的受剪性能试验研究

为研究高温后型钢再生混凝土梁的受剪性能,考虑再生粗骨料取代率、温度、混凝土强度等级3个变化参数,设计了17个试件进行不同高温后的静力加载试验。通过试验测试到不同高温型钢再生混凝土梁的物理及力学性能指标,并观察了该类梁高温后的受力破坏过程及形态,获取了其极限承载力以及受力破坏全过程的荷载-挠度曲线等重要资料,并分析了各变化参数对高温型钢再生混凝土梁的初始刚度、峰值荷载、延性系数及能量耗散的力学性能指标的影响规律。研究结果表明:随着温度的升高,型钢再生混凝土梁的质量变轻、初始刚度和峰值荷载降低,延性系数、能量耗散值则先减小再增大。取代率对各力学性能指标影响不大。随着混凝土强度的增大,初始刚度和峰值荷载增大,延性系数变小,能量耗散值基本不变。     

CFRP抗剪加固钢筋混凝土梁的耐火性能试验研究

采用厚型防火涂料对4根碳纤维布抗剪加固钢筋混凝土梁和1根对比梁进行了IS0834标准升温条件下的恒载升温耐火性能试验,得到了试验梁的测点温度、位移随时间增加的分布关系.分析了不同加载方式、剪跨比、加固量和防火保护层厚度对高温下CFRP抗剪加固梁的跨中挠度、破坏形态及耐火极限的影响.试验结果表明:在相同的弯、剪富余量,相...     

普通螺栓受剪承载力计算公式的讨论

本文对《钢结构设计规范》（ＧＢＪ１７—８８）中普通螺栓受剪承载力的计算公式进行了分析，对该公式的应用条件提出了补充建议。     

Experimental study on mechanical properties of high-strength fire-resistant steel at elevated temperatures

为研究高强耐火钢在高温下的力学性能，通过国产Q345FR、Q420FR、Q460FR耐火钢的高温下稳态拉伸试验和热膨胀变形试验，得到了20~800℃下各等级耐火钢的破坏模式、应力-应变关系曲线、力学性能参数及热膨胀系数，并与普通结构钢高温性能以及欧洲、中国的抗火设计规范的相关规定进行了对比。研究结果表明：在温度低于350~400℃时，国产高强耐火钢屈服强度、抗拉强度高于常温的，当温度超过400℃后，屈服强度、抗拉强度开始快速下降；欧洲规范EC3中给出的高温下普通结构钢的弹性模量、强度计算公式不适用于高强度耐火钢；温度低于450℃时，耐火钢试验值与GB 51249—2017《建筑钢结构防火技术规范》中普通钢取值更吻合；温度高于450℃时，耐火钢试验值与规范GB 51249—2017中耐火钢取值更吻合。针对Q345FR、Q420FR、Q460FR高强耐火钢，提出了高温下弹性模量、屈服强度、抗拉强度变化系数拟合公式，可用于耐火钢结构抗火设计。     

Q460高强钢螺栓连接承载性能试验研究

通过对20个Q460高强钢螺栓连接的静力拉伸试验,研究高强钢材料强度和螺栓布置方式对连接承载力和变形的影响。根据力平衡和变形协调条件建立方程,理论分析高强度钢材螺栓连接的受力性能,考察相关规范的适用性。结果表明：螺栓横向布置时,试件的承载力和变形随间距增大而增大;边距由1.5d0增大到2d0,端距由2d0增大到2.5d0时,试件极限承载力仅提高了0.78%和2.37%,说明达到标准构造取值后,边距和端距增大对连接的承载力影响甚微。螺栓纵向布置时,试件的承载力仅随边距增大呈线性增大趋势。钢板承压强度设计值取1.26fu,对于Q460高强度钢材其取值偏小。为国产高强度钢材螺栓连接的设计理论和方法提供了科学依据。     

Q690D高强钢螺栓连接疲劳性能试验研究

为探究Q690D高强度钢材螺栓连接的疲劳性能,对Q690D高强钢母材、有孔板和螺栓连接三组试件进行疲劳试验,拟合了S-N设计曲线,并与现行规范进行比较,对其疲劳特性及疲劳寿命给予评价。试验结果表明：Q690D高强钢母材、有孔板、螺栓连接疲劳极限比GB50017理论计算值分别提高了170%、76.02%、47.76%,比AISC360理论计算值分别提高了200%、131.77%、70.49%,说明Q690D高强钢螺栓连接具有较高的抗疲劳能力。讨论了应力集中与螺栓预紧力对试件疲劳强度的影响,应力集中系数越大,疲劳强度越小,螺栓预紧力能缓和应力集中程度,可间接提高疲劳寿命。基于零塑性累积应变率假设得到了疲劳损伤公式,应力集中在一定程度上可以反应损伤发展,损伤曲线可以解释疲劳破坏机理。     

Research on performance of high-strength bolted connection in fire and after fire

Experiments on the tensile performance and the shear performance in high temperature and shear performance after fire have been carried out to study the fire-resistant performance of high-strength bolted connection. The experimental research on the shear performance of the connection in high temperature reveals the effect of temperature on the mechanical performance of high-strength bolted steel. A formula for the mechanical performance index can be obtained through a comparative analysis. The research on the shear performance of high-strength bolt in high temperature presents the effect of temperature on the bolt's sliding load and limit load. The formula for calculating the sliding load and limit load for shear connection at high temperature can be put forward through a comparative analysis on the basis of the test results. The test results for the shear property of post-firing high-strength bolted connection reveal the change law of the sliding load in different fire temperatures, fire processing methods and types of cooling. Moreover, the calculation formula of the reduction coefficient of the sliding load is given. Research findings provide theoretical basis for research on fire-resistant performance of steel structure joints and the prerequisite for overall fire-resistant design of steel structures and act as an important reference for compiling and revising relevant codes. This paper can promote the improvement and development of fire-resistant design methods of steel structures.     

模块化装配式多高层钢结构全螺栓连接节点静力及抗震性能试验研究

为研究模块化装配式多高层钢结构的全螺栓梁柱连接节点的受力性能,采用GB 50017-2003《钢结构设计规范》中的设计方法,设计了4个该类型节点,对其进行了静力、滞回性能试验和有限元分析,获得了节点的静力性能和滞回性能、骨架曲线、延性性能、转动能力、刚度退化等。结果表明：焊缝质量、板件厚度、螺栓布置等因素对节点破坏模式和各项力学性能影响较大,在弦杆与柱座间的焊缝不过早断裂以及盖板与弦杆接触面不滑移的条件下,该类节点转动刚度较大,节点的承载能力高,延性、耗能能力、塑性转动能力较好。减小桁架梁弦杆和腹杆厚度会显著降低节点承载能力,但对节点的延性性能和耗能能力影响不大。     

Application of fire-resistant steel to beam-to-column moment connections at elevated temperatures

This paper presents a new method of using fire-resistant steel to improve the fire-resistance of beam-to-column moment connections in steel structures. Two full-scale beam-to-column moment connection specimens were tested at elevated temperatures according to the standard ISO-834 fire to verify the feasibility of the proposed method. In addition, a detailed 3-D finite element model was developed to simulate the structural behavior of the column-tree moment connection specimens in fire. The fire test results show that the proposed method can effectively extend the fire endurance time, reduce structural deformation, and raise the critical temperature to failure for the beam-to-column moment connections. The numerical results obtained from the 3-D finite element analyses for the two specimens successfully simulated the fire test results.     

Tests of single shear bolted connections of thin sheet steels at elevated temperatures—Part I: Steady state tests

The current design rules on bolted connections of thin sheet steels for cold-formed steel structures are applicable for ambient temperature condition only. Investigation of single shear bolted connections at elevated temperatures is limited. In this study, 120 single shear bolted connection specimens involving three different thicknesses of thin sheet steels and 30 coupon specimens were conducted by using steady state test method in the temperature range from 22 to 900 °C. There are three main failure modes observed in the single shear bolted connection tests, namely the net section tension, bearing, and tear out. The test results were compared with the predicted values calculated from the American, Australian/New Zealand and European specifications for cold-formed steel structures. In calculating the nominal strengths of the connections, the reduced material properties were used due to the deterioration of material at elevated temperatures. It is shown that the strengths of the single shear bolted connections predicted by the specifications are generally conservative at elevated temperatures. The comparison between the deterioration of the tested connection strengths and that of the material properties at elevated temperatures showed a similar tendency of reduction.     

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.     

State-of-the-art on resistance of bearing-type bolted connections in high strength steel

With the recent development of material science, high strength steel (HSS) has become a practical solution for landmark buildings and major projects. The current codes for design of bearing-type bolted connections of steel constructions were established based on the research of conventional steels. Since the mechanical properties of HSS are different from those of conventional steels, more works should be done to develop the appropriate approach for the design of bearing-type bolted connections in HSS. A review of the research carried out on bearing-type bolted connections fabricated from conventional steel and HSS is presented. The up-to-date tests conducted at Tongji University on four connection types fabricated from three grades of HSS with nominal yield strengths of 550, 690, and 890 MPa are presented. The previous research on failure modes, bearing resistance and the design with consideration of bolt hole elongation are summarized. It is found that the behavior of bolted connections in HSS have no drastic difference compared to that of conventional steel connections. Although the ductility is reduced, plastic deformation capacity of HSS is sufficient to ensure the load redistribution between different bolts with normal construction tolerances. It is also found that behavior of each bolt of multi-bolt connections arranged in perpendicular to load direction is almost identical to that of a single-bolt connection with the same end distance. For connections with bolts arranged in parallel to load direction, the deformation capacity of the whole connection depends on the minimum value between the end distance and the spacing distances in load direction. The comparison with existing design codes shows that Eurocode3 and Chinese GB50017-2017 are conservative for the design of bolted connections in HSS while AISC 360-16 may overestimate the bearing resistance of bolted connections.