An inelastic model for low cycle fatigue prediction in steel braces

This paper presents a nonlinear inelastic cyclic model to predict the effect of low cycle fatigue on the behavior of steel brace elements. This brace element is assumed as a beam-column element with pinned ends and a plastic hinge at mid-span. The kinematic hardening rule, based on the concept of a yielding surface in the theory of plasticity, together with the tangent modulus of elasticity, have been taken into account. Furthermore, a simplification of the linear cumulative damage theory is used to represent the low cycle fatigue deterioration of the brace element during the inelastic cyclic behavior. In the presented method, as an expansion of physical model theory, the governing yield function of the plastic behavior of the brace element is transformed mathematically by different factors. Then the yield surface which is defined in resultant stresses space, is changed and diminished by separately altering the axial load and bending moment terms of the yield function in each step of loading history to manifest low cycle fatigue deterioration. Comparison of the results of the proposed model with two existing experimental results has shown that this model was capable of predicting the low cycle fatigue of brace elements, and in one example, the rupture point of the brace element was predicted well by the model. It is advised that the model should be further expanded to more precisely include the effect of local buckling and distortion of brace elements with different cross-sectional geometries at the plastic hinge.     

New method of inelastic buckling analysis for steel frames

In general, the concept of bifurcation stability cannot be used to evaluate the critical load of typical steel frames that have geometric imperfections and primary bending moment due to transverse loads. These cases require a plastic zone or plastic hinge analysis based on the concept of limit-load stability instead. However, such analyses require large computation times and complicated theories that are unsuitable for practical designs. The present paper proposes a new method of inelastic buckling analysis in order to determine the critical load of steel frames. This inelastic analysis is based on the concept of modified bifurcation stability using a tangent modulus approach and the column strength curve. Criteria for an iterative eigenvalue analysis are proposed in order to consider the primary bending moment as well as the axial force by using the interaction equation for beam-column members. The validity and applicability of the proposed inelastic buckling analysis were evaluated alongside elastic buckling analysis and refined plastic hinge analysis. Simple columns with geometric imperfections and a four-story plane frame were analyzed as benchmark problems. The results show that the proposed inelastic buckling analysis suitably evaluates the critical load and failure modes of steel frames, and can be a good alternative for the evaluation of critical load in the design of steel frames.     

相邻施工对建筑物的影响性分析

针对相邻建筑物裂缝的产生、变形等现象,结合一工程实例,分析了在建建筑物施工对相邻建筑物的影响,提出了可靠的预防措施,以期减少工程施工对相邻建筑物的危害,从而保证了居民的生命财产安全。     

Practical advanced analysis software for nonlinear inelastic dynamic analysis of steel structures

This paper presents a practical advanced analysis software which can be used for nonlinear inelastic dynamic analysis of space steel structures. The proposed software can predict accurately the nonlinear response of a steel structure by using only one element per member in structural modeling. Three types of element including both geometric and material nonlinearities are implemented in the proposed software: (1) catenary cable element; (2) truss element; and (2) beam-column element. An incremental-iterative solution scheme based on the Newmark method and the Newton-Raphson method is adopted for solving the nonlinear equations of motion. Several numerical examples are presented to verify the accuracy and efficiency of the proposed software in predicting the nonlinear response of steel structures. The proposed program is shown to be an efficient and reliable tool for daily use in design.     

Buckling and cyclic inelastic analysis of steel tubular beam-columns

An numerical procedure combining the Finite Segment Method (FSM) with the Influence Coefficient Method (ICM) is presented for estimating the inelastic behaviour of steel tubular beam-columns under post-buckling and cyclic loading conditions. This combination takes the advantages of FSM and ICM, overcoming the difficulties encountered in numerical analysis at the stages of buckling and post-buckling. The effects of initial imperfections, residual stresses, and end-restraints are taken into account. Generalized stress-strain relationships are used in the analysis. Complete results obtained for a pin-ended beam-column are discussed and compared with available theoretical results.     

相邻建筑沉降观测的实践与成果分析

论述了相邻建筑沉降观测的意义，结合工程实例，对其观测成果进行了分析，得出了高层建筑施工对周围区域影响较大的结论，提出了设计方案充分考虑相邻建筑沉降问题的建议。     

Nonlinear inelastic analysis of concrete-filled steel tubular frames

This paper presents a reliable numerical procedure for the nonlinear inelastic analysis of concrete-filled steel tubular frames. Geometric nonlinearities are taken into account by the use of stability functions derived from the exact stability solution of a beam–column subjected to axial force and bending moments. The spread of plasticity over the cross section and along the member length is captured by tracing the uniaxial stress–strain relationships of each fiber on the cross sections located at the selected integration points along the member length. The nonlinear equilibrium equations are solved using an incremental-iterative scheme based on the generalized displacement control method because of its general numerical stability and efficiency. The accuracy of the proposed procedure is verified by comparisons of the obtained results with experimental data and existing solutions. The proposed numerical procedure proves to be a reliable tool for the nonlinear analysis of concrete-filled steel tubular structures.     

建筑用耐火钢

本文简要介绍了耐火钢的力学性能标准、微观组织及国内外的发展状况.国内耐火钢在开发和应用中存在的一些问题以及现有成果、并指出,同时具有耐候、耐蚀、耐火性能的铜种将成为建筑结构钢的发展方向.     

Uncertainty assessment of field weld connections and the related effects on service life of steel buildings

Abstract

Delay in construction schedules has raised concerns regarding the quality of field weld connections. To address this issue, the effects of field weld quality are evaluated using test data and literature review. The evaluation provides evidence supporting the assumption that for the marginal workmanship quality, the strength of steel connections can reduce by approximately 5%. The effects are then used to predict the service life of 9-story and 20-story steel buildings with pre-Northridge connections. The prediction adopts a seismic risk-based framework, and considers the uncertainties of steel material and workmanship quality. The example buildings are highly vulnerable to earthquake damage owing to their lack of connection ductility. That also amplifies the effects of poor field weld quality. The result indicates that in the case of marginal quality workmanship, the service life can be reduced by 20?years, with taller buildings more significantly affected.     

基于灰色-马尔柯夫链模型的建筑物变形分析与预报

变形监测数据的分析和预报一直是建筑物施工及运营管理中的重要内容,其预报的可靠性在很大程度上取决于正确选择科学的预测方法.本文在分析现有建筑变形预测方法的基础上,针对灰色系统理论中的GM(1,1)预测的局限性,通过状态划分及计算马尔柯夫转移概率矩阵的方法,提出了适合于建筑物变形预测的灰色-马尔柯夫链模型,同时对该模型进行...     

Non-linear inelastic analysis of steel arches at elevated temperatures

An innovative non-discretisation mechanical-based method is developed in this paper to analyse a steel arch at elevated temperatures so that its behaviour can be quantified. The steel arch has a generic but singly-symmetric cross-section with elastic and plastic parts, and it is subjected to an arbitrary thermal profile which varies along the length of the arch as well as through the depth of the cross-section. The effects of geometric and material non-linearity as well as potential catenary action which can occur at high temperatures are taken into account in the formulation. The efficiency and accuracy of the generic model developed is demonstrated by a comparison with a finite element model undertaken using ABAQUS. The proposed method is then utilised to elucidate some significant factors, such as the magnitude of the temperature at bottom fibre of the cross-section as well as the ratio of the temperature at the top fibre to that at the bottom fibre, on the response of a steel arch member during fire loading. The proposed model provides a computationally superior formulation to that of commercial finite element packages, and forms a platform which can be used for structural steel arch design and evaluation in the development of codified approaches to fire design on a performance basis.     

CFG桩对临近建筑的影响分析与研究

通过建立模型,分析了CFG桩对临近建筑的影响范围,并结合工程实例,对CFG桩施工后建筑物出现的裂缝问题进行了原因探讨,指出开挖基坑施工与施工后开挖基坑的顺序不同,对建筑物的影响范围与程度也不同,且CFG桩机施工时提钻速率对周边土体也有影响。     

Practical second-order inelastic analysis for three-dimensional steel frames subjected to distributed load

A practical second-order inelastic analysis of three-dimensional steel frames subjected to distributed load is developed. This analysis realistically assesses both strength and behavior of a structural system and its component members in a direct manner. To capture second-order effects associated with P−δ and P−Δ, stability functions are used to minimize modeling and solution time. The Column Research Council (CRC) tangent modulus concept is used to account for gradual yielding due to residual stresses. A softening plastic hinge model is used to represent the degradation from elastic to zero stiffness associated with development of a hinge. In proposed analysis, a member has two elements and three nodal points. A plastic hinge location can be captured in analysis as the internal nodal point traces the maximum moment location at each load step. Maximum moments and load–displacements predicted by the proposed analysis compare well with those given by other approaches.     

A modified dynamic inelastic analysis of tall buildings considering changes of dynamic characteristics

Pushover analysis is commonly used to evaluate the inelastic ultimate capacity of structures. However, pushover analysis is carried out based on constant distributions throughout the incremental analysis, which cannot capture the variation in the acceleration profile due to inelastic behavior. For this reason, when plastic hinges form in structure, constant distributions of lateral forces cannot be used any longer. Conventional dynamic inelastic method by time‐history analysis can be used for specific earthquakes to consider the changes in the distribution of lateral forces. This alternative approach, however, is not practical due to the volume of calculations required. In this study, MOdified Dynamic Inelastic Analysis (MODIA) is introduced to capture a distribution proportional to changing mode shapes affected by the change of stiffness. In this method, as a structure enters into the inelastic range, the distribution of lateral forces is changed according to the mode shapes of structure. The efficiency of the proposed method is verified by comparing the results from DRAIN. A 7‐story moment resisting frame and a 36‐story existing structure were analysed by both methods. The comparison showed a good agreement. The story shear–drift relationship, base shear, drift, ductility and overturning moment for the structures are also evaluated. Copyright © 1999 John Wiley & Sons, Ltd.     

深基坑开挖对相邻建筑影响分析

通过对某已建办公大楼在相邻建筑深基坑的开挖过程的侧斜、水位观测和沉降观测,分析了已建办公大楼地面、墙体严重裂缝的原因,结合分析结果,指出在设计基坑时要充分估计环境效应问题,及时控制其环境条件的变化,要充分重视和考虑地基水的渗流问题等。     

A computer method for nonlinear inelastic analysis of 3D semi-rigid steel frameworks

This paper presents an efficient computer method for inelastic and large deflection analysis of steel space frames with non-linear flexible joint connections, based on the most refined type of second order inelastic analysis, the plastic zone analysis. The method employs modeling of structures with only one element per member, which reduces the number of degree of freedom involved and the computational time. Gradual yielding of cross-sections is modeled using the nonlinear inelastic force strain relationships, and then using the flexibility approach the elasto-plastic tangent stiffness matrix and equivalent nodal loads vector of 3-D beam-column element is developed. The method ensures also that the plastic bending moment is nowhere exceeded once a full plastified section develops. A zero-length rotational spring element is used for incorporating the connection flexibility into the element tangent stiffness matrix and equivalent nodal forces. The combined effects of material, geometric and connection behaviour nonlinearity sources are simulated into an object oriented computer program automatically. This program was used to study the ultimate response of several steel frames, which have been studied previously by other researchers. The example of computations and the comparisons made have proved the robustness, accuracy and time saving of the proposed analysis method.     

地铁运行引起邻近建筑物振动的实测与分析

通过对地铁邻近建筑物的振动响应进行现场实测及数据分析,探讨了建筑结构各楼层的振动加速度响应,得出了地铁运行引起环境的振动在邻近建筑结构中的传播规律。     

紧邻历史保护建筑深基坑设计实践及监测分析

介绍了上海外滩源33号项目地下3层深基坑的工程概况,该基坑具有规模较大、周边环境复杂、地质条件较差及工期紧等特点。针对本基坑的特点,对历史保护建筑和古树采取了预保护措施,采用逆作法、管幕法等方法辅以节点加固、设置临时支撑等措施,取得了不错的工程效果。本工程监测数据的分析结果可为今后类似工程提供参考。     

邻近建筑物控制爆破技术

以李家营车站为例,对邻近建(构)筑物的路基石方开挖进行了控制爆破设计,爆破结果表明对邻近建(构)筑物的影响在可控范围内,且边坡平整度达到了预期效果,取得了创造性成果。     

A structural satefy analysis of steel buildings during construction

The safety of steel building during construction is evaluated. At each stage of construction, the potential modes of failure are identified and formulated for reliability analysis. The principal loading of concern is the maximum wind load over the critical stages of construction. Uncertainties associated with the properties of the structure at each stage of construction, and the wind environment parameters, are included in the formulation. The dynamic effect of wind on an incomplete frame is evaluated using elements of random vibration. The reliability of a ten-story steel frame building, built by a common combination of crew and equipment, is examined in detail.