考虑抗力修正系数和静载试验效率的#br# RC简支梁桥限载取值

为确定静载试验验证后钢筋混凝土简支梁桥的限载取值,提出一种考虑抗力修正系数和静载试验效率的钢筋混凝土简支梁桥限载分析方法。首先,以桥梁设计活恒载比值为基本参数,建立抗力下限值与验证荷载间的关系式,并构造考虑抗力左截尾数分布特征的限载分析模型。进而,根据钢筋混凝土梁抗弯承载能力设计表达式,计算与不同抗力修正系数和静载试验效率对应的结构安全等级一级桥梁限载系数。最后,通过分析现行规范桥梁汽车荷载效应与典型车辆荷载效应比值,提出典型五轴车辆的限载建议值。结果表明：抗力修正系数和荷载效率对桥梁限载取值有较为明显的影响;在相同设计活恒载比值下,抗力修正系数和静载试验效率越大,试验验证后桥梁容许的典型车辆总重限值也就越高;研究成果可为静载试验后桥梁的限载取值提供依据。     

基于规范车辆荷载模型的三塔悬索桥中间塔鞍座抗滑安全评估

中间塔鞍座抗滑安全是三塔悬索桥设计的关键问题之一,其特点与传统两塔悬索桥不同.根据鞍座与主缆间的抗滑力学模型,中间塔两侧的不平衡车辆荷载是导致主缆与鞍座滑移的主要因素.由于三塔悬索桥体系存在明显的几何非线性特性,通过分析明确了对于中间塔抗滑问题,不考虑车辆荷 .载的几何非线性是偏安全的,于是可选用基于叠加原理的线性理论计算车辆荷载效应.基于规范车辆荷载模型的中间塔鞍座抗滑安全评估表明,不同规范标准下的车辆荷载都能保证中间塔鞍座的抗滑安全,但相应的抗滑安全水平存在差异.因此为获取更加精细化的评估结果,有必要在桥梁实际工作状态下开展进一步的研究.     

A practical multi-lane factor model of bridges based on multi-truck presence considering lane load disparities

Many bridge design specifications consider multi-lane factors (MLFs) a critical component of the traffic load model. Measured multi-lane traffic data generally exhibit significant lane disparities in traffic loads over multiple lanes. However, these disparities are not considered in current specifications. To address this drawback, a multi-coefficient MLF model was developed based on an improved probabilistic statistical approach that considers the presence of multiple trucks. The proposed MLF model and approach were calibrated and demonstrated through an example site. The model sensitivity analysis demonstrated the significant influence of lane disparity of truck traffic volume and truck weight distribution on the MLF. Using the proposed approach, the experimental site study yielded MLFs comparable with those directly calculated using traffic load effects. The exclusion of overloaded trucks caused the proposed approach, existing design specifications, and conventional approach of ignoring lane load disparity to generate comparable MLFs, while the MLFs based on the proposed approach were the most comprehensive. The inclusion of overloaded trucks caused the conventional approach and design specifications to overestimate the MLFs significantly. Finally, the benefits of the research results to bridge practitioners were discussed.     

大型超市楼面活荷载的调查与统计分析

对大型超市(欧尚超市)楼面活荷载进行了调查,收集了大量的楼面活荷载资料。采用单位面积平均荷载法和进深板带面积平均荷载法分别将楼面持久性活荷载和楼面临时性活荷载等效为楼面均布荷载,给出了楼面持久性活荷载和楼面临时性活荷载的计算结果。利用数理统计方法,研究了大型超市楼面持久性活荷载和临时性活荷载的概率分布和统计参数,建立了设计基准期T=50年时楼面持久性活荷载和楼面临时性活荷载的概率分布模型,并确定了模型参数。在此基础上,提出了我国大型超市楼面活荷载标准值的建议取值。     

Methodology for development of live load models for refined analysis of short and medium-span highway bridges

Abstract

The accuracy of bridge system safety evaluations and reliability assessments obtained through refined structural and finite element analyses depends not only on the accuracy of the structural model itself but also on the proper modelling of the maximum traffic loads. While current code-specified live load models were calibrated to properly reflect the safety levels of bridge structures analysed using the simplified methods adopted in bridge design and evaluation manuals, these load models may not lead to accurate results when implemented during refined structural analysis procedures. This paper describes a method to calibrate appropriate live load models that can be used for advanced analyses of bridges. The calibration procedure is demonstrated using actual traffic data collected at a representative weigh-in-motion station in New York State. The proposed calibration methodology is applicable for developing live load models for different bridge service periods, bridge types and design/assessment codes or standards. Live load models obtained using the proposed calibration procedure are readily implementable for deterministic refined analyses of highway bridges to produce similar results to those of complex traffic load simulations. Examples are presented that describe how results of such calibrated live load models would be used in engineering practice.     

基于区间方法的活荷载不利分布计算

用区间有限元方法求解活荷载不利分布问题,在INTLAB[1]基础上完成了求解活荷载不利分布的区间有限元MATLAB程序,算例初步验证了该方法的可行性与准确性.研究了平面框架在不同层数、跨数及活荷载大小的情况下,活荷载的不利分布对梁弯矩的影响程度.算例表明:活荷载大小和框架层数是决定是否考虑活荷载不利分布的重要因素,特别对于高层建筑结构,随着层数增加活荷我的不利分布对梁端弯矩的影响程度显著增大,工程设计中应给予考虑.     

Effect of secondary elements on bridge structural system reliability considering moment capacity

Secondary elements such as barriers, sidewalks, and diaphragms may increase the load carrying capacity of girder bridges. This in turn affects reliability. The objective of this study is to evaluate the potential benefit of secondary elements on the system reliability of girder bridges, if these elements are designed with the structural system to participate resisting vehicular live loads. Simple span, two lane structures are considered, with composite steel girders supporting a reinforced concrete deck. For structural analysis, a finite element procedure is developed that combines a grillage model of the bridge deck with solid elements for edge-stiffening effects. Random variables considered are composite girder, barrier, and sidewalk flexural strengths (each in turn composed of many random variables), load magnitude (dead load and truck traffic live load), and live load position. System resistance parameters are estimated with a point integration method. System resistance is evaluated in terms of maximum load carried at ultimate capacity. It was found that the interaction of typical secondary element combinations has a varying effect on system reliability, depending on element stiffness, bridge span, and girder spacing.     

A Heuristic Approach for Interactive Analysis of Bridge Trusses under Moving Loads

A heuristic approach is presented for interactive analysis of statically determinate and indeterminate bridge trusses subjected to moving loads such as the American Association of State Highway and Transportation Officials (AASHTO) specifications live loads. These loads consist of two-axle truck loading, two-axle truck plus one-axle semitrailer loading, and uniform lane loading. The procedure is based on using the information about the shape of the influence line diagrams (ILDs) for members of a truss. This information may be obtained through numerical experimentation for any given type of truss. A methodology is presented for classifying the ILDs for member axial forces of a bridge truss. The procedure is applied to Pratt trusses. Heuristic rules are developed for finding the maximum compression and tensile forces in the members of a Pratt truss based on its characteristic influence line diagrams and the type of the AASHTO live load. The procedure presented in this article results in substantial savings in structural analysis computations, and is specially suitable on microcomputers in an interactive environment.     

Regression models for estimating storm runoff load and its application to Lake Kasumigaura

Regression models are proposed for accurate estimation of storm runoff load. Regression equations are obtained for the relationship between final cumulative load and flow during direct runoff by each storm event. The models are applied to estimate annual nutrients load by all influent rivers into the Lake Kasumigaura for a model year of average annual rainfall. The load in dry weather is calculated from observed data of all influent rivers. Total annual load for a year is the sum of loads in dry weather days and loads in wet weather days. The ratios of the load in a wet weather day to total annual loads are 29 percent for T‐N, 51 percent for T‐P, 53 percent for T‐COD, 22 percent for D‐N, 22 percent for D‐P and 30 percent for D‐COD.     

考虑全梁承载能力因素的RC桥梁限载取值

为确定85和04规范钢筋混凝土简支梁桥限载标准，系统分析了受弯和受剪抗力对桥梁限载系数的影响规律。首先，根据结构可靠度理论，提出了桥梁限载取值的一般分析方法。然后，以6～30m简支梁桥为例，通过比较85和04规范汽车荷载产生的跨中弯矩和支点剪力，选择三轴和五轴载重汽车作为典型限载车辆模型。在此基础上，以设计活恒载比值为基本参数，采用85和04规范钢筋混凝土受弯和受剪抗力设计表达式，分别计算了85规范汽车-20级和汽车-超20级以及04规范公路-Ⅰ级和公路-Ⅱ级桥梁的限载系数。结果表明，在同一限载安全等级下，按85和04规范设计的中、小跨径钢筋混凝土简支梁桥，其限载值均由受弯抗力控制，建议按受弯抗力确定此类桥梁的限载取值。     

Live load distribution equations for integral bridge substructures

In this study, live load distribution equations (LLDEs) for integral bridge (IB) substructures are developed. For this purpose, numerous 3-D and corresponding 2-D structural models of typical IBs are built and analyzed under AASHTO live load. In the analyses, the effect of various superstructure and substructure properties such as span length, girder spacing, girder stiffness, abutment height, pile size, pile spacing and foundation soil stiffness are considered. The results from the 2-D and 3-D analyses are then used to calculate the live load distribution factors (LLDFs) for the abutments and piles of IBs as a function of the above mentioned properties. LLDEs are then developed to estimate the live load moments and shear in the abutments and piles of IBs using these LLDFs and nonlinear regression analysis methods. It is observed that the developed LLDEs yield a reasonably good estimate of live load moment and shear in the abutments and piles of IBs.     

Live load factors for parking garage members

This paper proposes a simplified, but effective, algorithm to obtain critical design moments for clamped and/or elastically supported parking garage girders, beams and slabs. Maintaining the uniformly distributed load concept, the equivalent vehicle load factors which can simulate vehicle load effects without conducting additional sophisticated numerical analyses for the concentrated loads are introduced. After determining a standard design vehicle of 2.4 tons through an investigation of small to medium-sized vehicles made in Korea, finite element analyses for concentrated wheel loads were carried out by referring to the influence lines for the girders and beams and influence surfaces for the slabs. Based on the obtained member forces, we determined the equivalent vehicle load factors for the girders, beams and slabs which represent the ratios of member forces under vehicle loads to those under uniformly distributed loads. In addition, the relationships between the equivalent vehicle load factors and sectional dimensions were established by regression and used to obtain the design moments by vehicle loads. The member forces calculated by the proposed method are compared with the results of different approaches mentioned in current design codes with the objective of establishing the relative efficiencies of the proposed method.     

Determination of accidental forklift truck impact forces on drive-in steel rack structures

The paper addresses the problem of determining the accidental forklift truck impact forces on steel storage racks. Based on first principles of mechanics, simple models of a loaded forklift truck and a drive-in racking structure are presented. Model masses, as well as stiffness and damping coefficients are calibrated against experimental results obtained from tests of a forklift truck and a drive-in racking structure. Comparisons between experimental results and solutions obtained from the simple mechanical models show that the simple models accurately reproduce the static and dynamic behaviours of their associated structures. Based on the drive-in rack impact test results presented in a companion paper (Gilbert and Rasmussen, submitted for publication) [1] and the simple mechanical models for drive-in racks, actual impact forces are calculated and presented. Finally, using the impact test results and the simple mechanical models, the actual motion of the forklift truck body is calculated. This motion, being a common characteristic to all drive-in racking impacts, allows impact forces to be obtained for various pallet loads, impact elevations and rack characteristics. Thus, the paper concludes with a general method for calculating forces generated under forklift truck impact.     

对我国住宅楼面活荷载概率模型的探讨

针对我国住宅建筑活荷载的统计参数与美国差别较大的问题。本文首先分析差别较大的原因;其次,应用比较方法确定我国楼面活荷载概率模型的参数;最后,应用数值模拟方法和等超概率原则确定不同设计基准期的楼面活荷载最大值。     

复合荷载作用下钢梁弯扭屈曲的临界弯矩: (Ⅱ)系数计算及数值算例

基于平面外4种边界约束条件简支钢梁在满跨均布荷载、跨中对称集中荷载和端弯矩作用下,以及平面外4种边界约束条件固支钢梁在满跨均布荷载、跨中对称集中荷载作用下的Mcr三系数(C1,i、C2,i、C3,i)计算式,计算了典型单一荷载工况的Mcr三系数数值,给出了横向荷载与端弯矩共同作用简支钢梁以及横向荷载两两共同作用固支钢梁的复合弯矩系数Cb计算式,通过数值算例验证了本文Mcr三系数和复合弯矩系数计算式的精度。最后对比了本文的Mcr三系数数值与EN 1999 1 1: 2007和ENV 1993 1 1: 1992中单一荷载的Mcr三系数数值,校验了“4M”等效弯矩系数计算式对简支钢梁、固支钢梁的适用性。结果表明：对于除平面外边界约束条件为R R(平面外两端简支且约束转动)外的单轴或双轴对称截面简支钢梁以及双轴对称截面固支钢梁,单一荷载的Mcr三系数的数值或计算式以及复合弯矩系数计算式均具有较高精度;EN 1999 1 1: 2007和ENV 1993 1 1: 1992中部分工况的C2,i和C3,i不精确;现有“4M”等效弯矩系数计算式仅能用于计算平面内外简支钢梁的Cb或C1,i。     

有效预应力作用下预应力砼超静定结构的次弯矩计算

本文提出的约束次弯矩法是直接由主弯矩计算预应力砼超静定结构的次奇矩，省去了常用的等效荷载法［１］［３］计算次弯矩时需计算等效荷载和综合弯矩这两个步骤，并能较准确计算考虑各种预应力损失后的有效预应力作用下的次弯矩，提高工程设计精度。     

Design concepts of an aircraft wing: composite and morphing airfoil with auxetic structures

This paper is categorized into two parts. (1) A frame work to design the aircraft wing structure and (2) analysis of a morphing airfoil with auxetic structure. The developed design frame work in the first part is used to arrive at the sizes of the various components of an aircraft wing structure. The strength based design is adopted, where the design loads are extracted from the aerodynamic loads. The aerodynamic loads acting on a wing structure are converted to equivalent distributed loads, which are further converted point loads to arrive at the shear forces, bending and twisting moments along the wing span. Based on the estimated shear forces, bending and twisting moments, the strength based design is employed to estimate the sizes of various sections of a composite wing structure. A three dimensional numerical model of the composite wing structure has been developed and analyzed for the extreme load conditions. Glass fiber reinforced plastic material is used in the numerical analysis. The estimated natural frequencies are observed to be in the acceptable limits. Furthermore, the discussed design principles in the first part are extended to the design of a morphing airfoil with auxetic structure. The advantages of the morphing airfoil with auxetic structure are (i) larger displacement with limited straining of the components and (ii) unique deformation characteristics, which produce a theoretical in-plane Poisson’s ratio of–1. Aluminum Alloy AL6061-T651 is considered in the design of all the structural elements. The compliance characteristics of the airfoil are investigated through a numerical model. The numerical results are observed to be in close agreement with the experimental results in the literature.     

BS5400规范中的荷载及荷载组合

结合对英国规范BS5400中有关荷载规定的理解，就对国内桥梁设计具有重大参考价值的内容，从恒载、二期恒载、活荷载、荷载组合等方面进行了介绍，对于大跨度桥梁横向的动力分析有很好的帮助。     

Probability-based patterned live loads for design

Probability-based patterned live loads for design are discussed with regard to probabilistic models of load-effects due to sustained live loads on floors. Statistics are presented for equivalent uniformly distributed loads (EUDLs) and equivalent patterned loads (EPLs) for a continuous beam and for continuous floor slab systems. It is shown that EPLs (rather than EUDLs) are required to realistically model structural load-effects that are sensitive to random load patterns. Furthermore, it is shown that an appropriate set of EPLs (for load-effects that are compounded by loading in the vicinity of the load-effect) can be approximated using a standardised EUDL (dependent on the area over which it acts) on the critical structural bay(s) in the vicinity of the load-effect, together with a constant (mean) uniformly distributed load acting on the other structural bays. Accordingly, ‘chequerboard’ design loads are not required. Indeed, it is shown that chequerboard EPLs are not appropriate for design, because their statistics are sensitive to the structural type and they are significantly different from the statistics of the standard EUDLs that are the basis of the standard design loads specified in design codes.