土木工程专业毕业设计-外文翻译-将玻璃钢外套用于钢筋混凝土框架结构 抗震加固的最优设计

河北工业大学

毕业设计(论文)外文资料翻译

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附件： 1.外文资料翻译译文；2.外文原文。

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附件1：外文资料翻译译文

将玻璃钢外套用于钢筋混凝土框架结构

抗震加固的最优设计

主题：

外包纤维增强高分子复合材料(玻璃钢)是一项正在完善的为强化/改造钢筋混凝土(RC)结构的技术, 尤其玻璃钢与钢筋混凝土柱隔离外套已经被证明能非常有效地提高了柱的强度和韧性,成为的钢筋混凝土结构抗震加固的关键技术但是大量的研究仅限于钢筋混凝土柱的力学性能、很少有研究含有FRP约束柱的钢筋混凝土框架的力学性能在用玻璃钢对钢筋混凝土框架结构进行抗震加固时,一个问题是框架结构的应力, 另外一个重要问题就是如何利用最少的材料及其用费达到所需的抗震性能.

从这两个问题出发, 本文讨论基于抗震设计性能出发的用玻璃钢外套加固钢筋混凝土建筑物优化技术. 我们采取玻璃钢外套厚度作为隔离柱设计变量因此,体积最小、材料成本最低就是是优化设计目标漂流的劝服是明确表示在使用的玻璃上浆变数,虚功原理泰勒级数的逼近.？？？？？最优准则(OC)的办法是采用非线性地震侧移的设计问题. 本文通过实例介绍和讨论,展示了该程序.

关键词:

约束；纤维增强聚合物(玻璃钢); 性能化设计; pushover分析; 钢筋混凝土; 抗震加固; 结构优化

1．介绍

在重力荷载下按旧规范设计装裱现有钢筋混凝土(RC)结构抗震性能或在最近的地震证明是不够的，横向承载能力有限,延性差[1] 这种结构具有一种内在的抵抗横向载荷能力低,地震期间造成很大塑性变形而且,结构特点是强梁弱柱，导致在地面强烈震动脆性破坏或柱侧向倾倒 [2] 。为了减少结构在强震倒塌的风险, 这就迫切需要提升现有的钢筋混凝土建筑物的抗震性能,以符合现行抗震设计规范. 钢筋混凝土建筑物的抗震加固的缺陷可能涉及的地区加强针对性,增强实力刚度和/或提高结构延性、或提供多余承载机制. 一般来说,各种技巧可以结合运用在结构的抗震加固. 具体加固改造策略选择的目标应该是基于经济考虑 [1] 加固设计

应以在指定震动下,确保没有损坏超过确定的程度或建筑物没有倒塌为适当的标准[3] 另外,实施的费用是业主和工程师都十分关心的[4] 整个钢筋混凝土框架抗震加固策略必须综合考虑的一系列关键问题。这些问题包括加强横梁, 柱和梁柱节点脆性破坏模式等, 用玻璃钢补强外部或其他适当方式以防止象剪切破坏的脆性破坏。一旦这些脆性破坏模式确定了，进行抗震加固的设计以满足地震强度要求，这取决于该柱下轴压和弯曲下的承载力和延性。改造柱是最广泛使用的提高钢筋混凝土框架结构抗震等级的办法改善柱子的力学性能通常涉及提高其强度,韧性、刚度、在大多数情况综合这些参数. 改造柱子常规措施包括加装铺混凝土或钢套管. 最近技术是利用纤维增强聚合物(玻璃钢)外套来限制柱侧向变形[5][6] 在这种外套, 纤维唯一或主要在法向约束混凝土,其抗压实力与最终压应变明显提高 [5]、[6]、[7]. 传统工艺相比,玻璃钢套管容易和更快地实施几乎不增加自重,对现行体制冲击微小并且抗腐蚀. 结果，玻璃钢套管已被发现比传统技术是一个更具成本效益的方法,因而,在许多情况被广泛接受[5]、[6]和[8].

用玻璃钢限制钢筋混凝土柱来对钢筋混凝土框架结构抗震加固, 除了加固结构的应力外、一个重要问题就是如何利用最少的玻璃钢材料达到所需的抗震等级. 这两个问题出发, 本文为优化技术性能的抗震设计的钢筋混凝土建筑物加装玻璃钢框. 玻璃钢外套的厚度在柱加固设计视为变量，而玻璃钢的最总材料成本(即费用等方面,不包括交通)作为一个统一的延性需求的弹性设计目标优化设计侧移的过程.

2．现有最优的抗震设计

传统抗震设计方法对现有建筑抗震加固, 类似用传统方法新结构进行抗震设计, 都假设弹性结构在甚至是严重地震下反应是弹性的，[9]. 基于地震反应的抗震设计,看来是抗震设计规范未来的发展方向, 直接指出在结构在地震作用下弹性变形是非弹性的 [3],[9],[10]. 在评估框架结构抗震性能的非线性后、 Pushover 分析日益被接纳作为性能化设计程序. Pushover分析是一个简化的、静态的、非线性的分析，在这个过程中预定的地震载荷模式逐步加到向结构,直到塑料破坏机制形成，结构崩溃. 这种方法采用理论分析,随菏载不断增加，裂缝随塑性变化在框架构件边缘形成塑性铰. 横向侧移性能是多层建筑一项重要指标,用来衡量不论在现有抗震设计方法还是当前的新发展表现为设计做法设计的建筑物结构性和非结构性部件损坏程度。 [1],[3],[9],[10]和[11]. 考虑在横向地震荷载下多层构

件弹性、非弹性变化对构件进行经济设计是相当有难度的、具有挑战性的任务[12] 横向侧移设计尤为艰巨,因为它需要考虑在严重的地震中适当分配各构件刚度而,以及各构件塑性内力重分布.

在缺乏自动优化技术情况下、钢筋的等级的数量是基于直觉和经验来设计的[12]. 需要一个优化设计方法是显而易见的, 过去数几十年间动态结构优化一直积极研究的课题。[12]、〔13〕、〔14〕、〔15〕、〔16〕、〔17〕、〔18〕. 近年来,许多研究已经致力于专门的优化性能设计方法. 尤其是成与邹[12], 邹、邹、陈[16][17]和[18]提出了基于弹性、非弹性侧移性能的钢筋混凝土建筑物抗震设计优化技术. 他们发现自动优化技术是用最价廉的设计实现了最佳抗震性能. .优化现有结构抗震加固设计的具体研究太有限了. 马丁-拉、罗梅罗[19]提出一个简单的解决方法,从而优化了非线性粘性流体阻尼改造框架地震弯矩.

就作者所知，改造策略是用玻璃钢外套限制隔离柱以对钢筋混凝土结构抗震加固，目前还没有做过这方面优化设计的研究. 目前, 用玻璃钢限制隔离柱性能化改造钢筋混凝土结构设计只能基于主观经验和大量运算工作的试错法设计. 最后的设计可能过于保守, 改造费用昂贵造成不必要的干预和抗震性能比降低. 本文讲述考虑侧移性能对建筑物钢筋混凝土框架抗震加固设计优化技术，填补了现有研究的一项空白.加固策略是基于用玻璃钢限制柱的两端, 即在塑性铰潜在形成区域加固 [20],[21],[22]和[23]. 优化设计过程是一个已从原先成和邹[12], 邹、、陈[16][17][18] 制定的抗震设计体系适度修正而来的.

3. 进一步的设计优化问题

图1、所示. 玻璃钢薄板用纤维圈从法向约束柱

.

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图1 ，柱抗震加固的玻璃钢外套约束区域

这项研究认为,一个钢筋混凝土框架结构潜在塑胶铰(假定每一个构件端部都存在一个铰) Nc柱、Nb梁, 2(Nc + Nb) 假定柱截面是长方形,宽度Bi和高度Di.由玻璃钢约束柱的潜在塑性铰区而取得抗震加固效果，如图. 1所示.

在这项研究中只有约束柱塑性铰玻璃外套的厚度被作为设计变量. 这种方法是现实的,同时也降低了设计的管理规模. 外套所需的厚度首先满足该构件的抗剪承载力[5]、但本文的优化设计程序中都没有讨论这些厚度. 在实际执行的抗震加固策略时,对任何一个柱子潜在的塑性铰区玻璃钢外套总厚度的应该是3种失效模式分别需要厚度的总和, [5].鉴于现阶段知识技术水平，这是一个保守而务实的考虑. 在优化过程设计变量,是厚度ti、即约束每个构件塑性铰的玻璃外套的厚度. 对于某一类玻璃钢材料如果拓扑结构是预先假定的每柱子有同样厚度的玻璃钢外套而同样长度的两端约束区域, 用于约束柱玻璃钢复合材料的总成本由下式给出：

(

1)

其中wi为玻璃钢复合材料成本系数、wi = 4Lci(Bi + Di)ρ; ρ为单位体积的玻璃钢复合材料的费用; Lc,是原来每个柱端部约束区域的长度,即最大的可能塑性铰长度、0.5D和构件长度12.5%中的较大值 [5][21]. 在实际执行过程中，与原先约束区域毗邻的二级约束区也应约束,但玻璃外套厚度减至原约束区的一半. 本文没有进一步考虑二级约束区所需玻璃钢材料费用金额.

附件2：外文原文

Optimal performance-based design of FRP jackets for seismic retrofit

of reinforced concrete frames

Abstract

External bonding of fiber-reinforced polymer (FRP) composites is now a well-established technique for the strengthening/retrofit of reinforced concrete(RC) structures. In particular, confinement of RC columns with FRP jackets has proven to be very effective in enhancing the strength and ductility of columns, and has become a key technique for the seismic retrofit of RC structures. Despite the large amount of research on the behavior of RC columns confined with FRP, little research has been conducted on the behavior of RC frames with FRP-confined columns. For the seismic retrofit of RC frames with FRP, apart from the structural response of a retrofitted frame,an important issue is how to deploy the least amount of the FRP material to achieve the required upgrade in seismic performance.

With these two issues in mind, this paper presents an optimization technique for the performance-based seismic FRP retrofit design of RC building frames.The thicknesses of FRP jackets used for the confinement of columns are taken as the design variables, and minimizing the volume and hence the material cost of the FRP jackets is the design objective in the optimization procedure. The pushover drift is expressed explicitly in terms of the FRP sizing variables using the principle of virtual work and the Taylor series approximation. The optimality criteria (OC) approach is employed for finding the solution of the nonlinear seismic drift design problem. A numerical example is presented and discussed to demonstrate the effectiveness of the proposed procedure.

Keywords:

Confinement; Fiber-reinforced polymer (FRP); Performance-based design; Pushover analysis; Reinforced concrete; Seismic retrofit; Structural optimization

1. Introduction

The seismic performance of existing reinforced concrete (RC) framed structures designed for gravity loads or according to old codes has proven to be poor during recent earthquakes, due to insufficient lateral

load-carrying capacity and limited ductility [1]. Such structures possess an inherently low resistance to horizontal loads, resulting in large inelastic deformations during earthquakes. Moreover, their structural

behavior is of the weak column/strong beam type, which results in brittle soft-story or column sideway collapse mechanisms during strong ground motions [2]. In order to reduce the risk of structural collapses during strong earthquakes, there is an urgent need to upgrade existing RC buildings to meet the requirements of current seismic design codes. The seismic retrofit of an RC building may involve targeted strengthening of deficient regions, to increase the strength, stiffness and/or ductility of the structure, or to provide redundant load-carrying mechanisms. In general, a combination of different techniques may be employed in the seismic retrofit of a structure. The selection of a specific retrofit strategy should be based on the retrofit objectives as well as on economic considerations [1]. The retrofit design should be based on appropriate performance criteria to ensure that a defined level of damage is not exceeded or the collapse of the building is prevented during specified ground motions [3]. In addition, the cost of implementation is of great concern to both building owners and practicing engineers [4]. The overall seismic retrofit strategy for an RC frame must consider a number of key issues in an integrated manner; these issues include the strengthening of beams, columns and beam-column joints to prevent brittle failure modes such as shear failure to become critical using external FRP reinforcement or other appropriate methods。Once these brittle failure modes are suppressed, the seismic retrofit design to enable the frame to satisfy specific demands of an earthquake depends on the strength and ductility of the columns under combined axial compression and bending. Retrofit of the columns is one of the most widely used seismic upgrading approaches for RC frames，Improving the column behavior typically involves increasing its strength, ductility, stiffness or in most cases a combination of these parameters. Conventional retrofit measures for columns include RC overlays or steel jacketing. A more recent technique is the use of fiber-reinforced polymer (FRP) jackets to confine columns [5] and [6]. In such jackets, the fibers are oriented only or predominantly in the hoop

direction to confine the concrete so that both its compressive strength and ultimate compressive strain are significantly enhanced [5], [6] and [7]. Compared to conventional techniques, FRP jacketing is easier and quicker to implement, adds virtually no weight to the existing structure, has minimal aesthetic impact and is corrosion-resistant. As a result, FRP jacketing has been found to be a more cost-effective solution than conventional techniques in many situations and has thus been widely accepted [5], [6] and [8]. For the seismic retrofit of RC frames employing FRP confinement of RC columns, apart from the structural response of a retrofitted frame, an important issue is how to deploy the least amount of the FRP material to achieve the required upgrade in seismic performance. With these two issues in mind, this paper presents an optimization technique for the performance-based seismic FRP retrofit design of RC building frames. The thicknesses of FRP jackets in the columns are considered as the design variables, while the least total material cost (i.e. costs associated with other aspects such as transportation are not included) of FRP and a uniform ductility demand are taken as design objectives of the inelastic drift design optimization process.

2. Existing work on optimal performanced-based seismic design

Traditional design approaches for seismic retrofit, similar to traditional approaches for seismic design of new structures, assume that structures respond elastically even to severe earthquakes [9]. Performance-based seismic design, which appears to be the future direction of seismic design codes, directly addresses inelastic deformations induced in structures by earthquakes [3], [9] and [10].

In assessing the nonlinear seismic behavior of framed structures, pushover analysis has been increasingly accepted as part of the performance-based

design procedure. Pushover analysis is a simplified, static, nonlinear procedure in which a predefined pattern of earthquake loads is applied incrementally to the structure until a plastic collapse mechanism is reached. This method of analysis generally adopts a lumped-plasticity approach that tracks the spreading of inelasticity through the formation of plastic hinges at the ends of the frame elements during the incremental loading process. The lateral drift performance of a multi-story building is an important indicator that measures the level of damage to the structural and

non-structural components of a building in current seismic design approaches and also in the newly developed performance-based design approach [1], [3], [9], [10] and [11]. The economic design of structural elements for various levels of elastic and inelastic lateral drift performance under multiple levels of earthquake loads is generally a rather difficult and challenging task [12]. Lateral drift design is particularly challenging as it requires the consideration of an appropriate stiffness distribution of all structural elements and, in a severe seismic event, also the occurrence and redistribution of plasticity in the elements. Structural engineers are thus faced with the problem of efficiently distributing materials throughout the structure to optimize the elastic and inelastic drift responses of structures. In absence of an automated optimization technique, sizes of members and amounts of steel reinforcement are designed by trial-and-error methods based on intuition and experience [12]. The need for an optimal design approach is thus clear, and structural optimization of dynamically excited structures has been an active research topic for the past few decades [12], [13], [14], [15], [16], [17] and [18] In recent years, much research has been devoted to the optimization of the emerging performance-based design approach. In particular, Chan and Zou [12], Zou [16]and Zou and Chan [17] and [18] proposed an optimization technique for elastic and inelastic drift performance-based seismic design of RC buildings. They showed that an automated optimization technique is capable of achieving the best seismic

drift performance combined with the least expensive design. Specific research on the optimization of seismic retrofit design of existing structures has been much more limited. Martinez-Rodrigo and Romero [19] proposed a simple methodology leading to an optimal solution with nonlinear viscous fluid dampers for the seismic retrofit of moment–resisting frames. To the best of the authors’ knowledge, no research has been conducted on the optimization of seismic retrofit design of RC structures when the retrofit strategy is the confinement of columns with FRP jackets. At the present, the performance-based retrofit design of RC structures with FRP confinement of columns can only be conducted by trial-and-error methods based on subjective experience and much computational effort. The final design may be overly conservative, resulting in an unnecessarily expensive retrofit intervention and less than optimal seismic performance. The optimization technique for the drift performance-based seismic retrofit design of framed RC buildings presented in this paper therefore fills a significant gap in existing research. The retrofit strategy is based on the FRP confinement of columns at the two ends, i.e. in the regions of potential plastic hinge formation [20], [21], [22] and [23]. The optimal design procedure is one that has been appropriately modified from that previously developed by Chan and Zou [12], Zou [16] and Zou and Chan [17] and [18] for the seismic design of new structures.

3. Optimal seismic retrofit design problem

3.1. Implicit design optimization problem

As shown in Fig. 1, FRP sheets for confinement of columns are wrapped around columns with the fibers oriented in the hoop direction. The consequent increases in the axial compressive strength and the ultimate axial strain of the concrete core depend on several factors, including the thickness,

tensile strength and elastic modulus of the confining FRP jacket, unconfined concrete strength and cross-sectional shape of the column [7]. For given material properties and cross-sectional dimensions, the thickness of the FRP jacket governs the strength and ductility of the confined cross-section.

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Fig. 1. FRP-jacketed regions of column for seismic retrofit.

This study considers an RC framed structure with N c columns, N b beams, and hence 2(N c + N b) potential plastic hinges (assuming one hinge at each end of each member). The column is assumed to have a rectangular cross-section, with width B i and depth D i. Seismic retrofit is achieved with FRP confinement of the potential plastic hinge regions of each column, as shown in Fig. 1. Only the thicknesses of the FRP jackets required for confinement of the plastic hinges are considered as design variables in this study.

This approach is realistic and also reduces the design problem to a manageable size. The jacket thicknesses required for shear resistance and for confinement of lap splices are first calculated for each member [5], but these thicknesses are not taken into account in the optimal design procedure presented in this paper. In practical implementation of the seismic retrofit strategy, for any potential plastic hinge region in a column, the total thickness of the FRP jacket should be the sum of those determined for the three failure modes, respectively [5]. This represents a conservative but realistic approach given the current stage of knowledge. The design variables in the optimization process are therefore the

thicknesses, t i, of the FRP jackets required for confinement of the plastic hinges in each member. For a given type of FRP material, if the topology of the structure is predefined and each column is assumed to have the same FRP jacket thickness and the same length of the confined region at both ends, the total material cost of the FRP composite used for column confinement is given by

(1)

where w i is the cost coefficient for the FRP composite, w i = 4L c i(B i + D i)ρ; ρ is the cost per unit volume of the FRP composite; and L c i is the length of the primary confinement region at each end of the i th column, which should be the largest of the plastic hinge length, 0.5D and 12.5% of member length [5] and [21]. In practical implementation, a secondary confinement region adjacent to the primary confinement region should also be confined but with the FRP jacket thickness reduced to half of that in the primary confinement region. The amount of FRP required for confining the secondary confinement region is not further considered in this paper.