Experimental study on scaling of RC beams under close-in blast loading

Damage effects analysis and assessment of buildings under blast loading is an important problem concerned by the area of explosion accident analysis, blast-resistant design, anti-terrorist and military weapon design.The damage character of RC beam under close-in blast loading is investigated through experiments. The damage modes and damage levels of RC beams are studied under different blast loads. The results show that the spallation area increases with the decrease of the scaled distance. The concrete beams are prone to be damaged in flexure mode with concrete crushed on the front face, concrete spallation on the back surface and concrete flake off on the side surface. The scaling of the dynamic response of reinforced concrete beams subjected to close-in blast loadings is also studied. The test results showed a similar macrostructure damage and fracture in all experiment conditions. But the local damage degree of RC beams with smaller size has been reduced a little as compared with that of beams with larger size. Based on the results, empirical equations of the center deflection to height ratio are proposed to correct scaling model considering size effects.     

建筑结构构件基于性能的抗爆设计方法

在我国,基于性能的设计方法已运用于工程结构抗震设计,但尚没有运用在结构抗爆设计。该文将基于性能的设计方法引入结构抗爆领域,提出了基于性能的结构抗爆设计方法,明确了基于性能的抗爆设计中的关键问题,给出了设计思路与步骤。在此基础上,以RC柱为研究对象,以轴心受压承载力损失为性能水平参数,划分了3个等级性能水平;根据典型的爆炸场景,确定爆炸的不同烈度等级,计算出RC柱承受的荷载;针对不同类别的建筑,确定两个水准的抗爆性能目标;结合现有RC柱承载力损失的研究成果,分析不同爆炸烈度下的RC柱的承载力损失,提出RC柱基于承载力损失的性能设计方法;基于确定的性能目标和设计方法,提出RC柱基于性能的抗爆设计步骤;最后,给出了RC柱基于性能的抗爆设计的算例。     

爆炸荷载作用下钢筋混凝土结构的动态响应与破坏模式的数值分析

在爆炸荷载(尤其是脉冲荷载)作用下,除了常见的弯曲破坏形态之外,钢筋混凝土结构还可能发生直剪破坏和弯剪破坏。如何准确地预测爆炸荷载作用下的钢筋混凝土结构动态响应和破坏特征是当前抗爆结构领域十分关注的课题之一。该文介绍作者近年来在这方面的一些研究成果,主要有:将三参数形式的应变速率型材料模型推广应用于二维状态下的混凝土本构关系,建立了弹粘塑性混凝土结构有限元分析方法;基于Timoshenko梁理论和弹粘塑性理论,分别采用有限差分法和有限元法,建立了土中浅埋钢筋混凝土结构动力响应和破坏模式的有限差分和有限元分析方法。对爆炸荷载作用下的典型钢筋混凝土结构计算结果表明:基于Timoshenko梁理论的有限差分分析方法和有限元分析方法能较好地模拟梁的动态响应和弯曲、弯剪以及直剪的破坏模式,而二维弹粘塑性混凝土结构有限元分析方法只能较好地模拟梁的弯曲破坏模式。     

A novel framework towards the design of more sustainable concrete infrastructure

This study presents a novel framework for the design of reinforced concrete (RC) structures which aims at ensuring that future RC structures have the lowest possible carbon footprint, energy use and impact on the environment. The key focus of the study is on RC structures where there is often a lack of grasp of materials aspects, and environmental aspects of construction. In the proposed framework, a set of quantifiable design parameters and variables (binder type, concrete grade, diffusivity, concrete cover depth, area of steel in the structural component) are selected with respect to a set of performance measures which cover the functionality and availability of the structure to the user during its service life. The outputs generated from the framework are optimised material types and properties which not only meet the design performance requirements but also lead to minimised life-cycle environmental impacts. A RC beam is used to demonstrate the proposed design methodology. The application of the framework for design in the material specifications of the RC beam showed a reduced volume of materials in construction compared to the current materials and structures design practice.     

Numerical study on damage mechanism of RC beams under close-in blast loading

RC structures have been widely used in civil engineering, and are vulnerable under blast loading. Improved understanding of damage mechanism of RC components helps advances the damage evaluation of RC structures under blast loading. In this paper, damage mechanisms of RC beam under close-in blast loading are investigated numerically. The FE model is validated through the experimental data reported by other researchers. A comprehensive investigation is carried out to investigate the damage mechanisms of RC beam, including the propagation of the main cracks, spallation at the bottom and the exfoliation of the side-cover concrete.     

基于分片响应面的钢筋混凝土梁变形随机模拟

将响应面与蒙特卡洛方法结合,可降低随机模拟的计算代价。但当钢筋混凝土梁所受荷载接近开裂荷载时,梁体的变形响应面形状将出现不光滑的现象。采用传统的单一响应面方法来描述结构响应将与实际产生明显的偏差。采用改进的分片响应面技术结合蒙特卡洛方法,建立了钢筋混凝土梁变形随机分析模型。以钢筋混凝土试验梁作为算例,讨论了分片参数的合理取值,并验证了方法的正确性。     

Mechanical performance of composite-strengthened concrete structures

The interest of using fibre reinforced plastic (FRP) materials in rehabilitating damaged concrete structures respectively has been increased rapidly in recent years. In this paper, the structural behaviours of the glass–fibre composite strengthened concrete structures subjected to uni-axial compression and three point bending tests are discussed through experimental studies. Two types of concrete structure are used in present study, they are concrete cylinder and rectangular concrete beam. Discussion on the environmental effects of composite strengthened reinforced concrete (RC) structures is also addressed. Experimental results show that the use of glass–fibre composite wrap can increase the load carrying capacity of the plain concrete cylinders with and without notch formation. The flexural load capacity of the concrete beam increases to more than 50% by bonding 3 layers of glass–fibre composite laminate on the beam tension surface. Direct hand lay up method gives better strengthening characteristic in term of the ultimate flexural load compared with pre-cured plate bonding technique. The flexural strengths of composite strengthened RC beams submerged into different chemicals solution for six months are increased compared with the RC beams without strengthening. The strength of the concrete structure is seriously attacked by strong acids.     

Residual axial compression capacity of localized blast-damaged RC columns

The risks associated with suitcase bombs are of serious concern because they can be easily handled and placed within close proximity of key structural components of building structures. The most common failure mode of the structures subjected to blast loads from satchel and suitcase bombs is progressive collapse. High-fidelity physics based computer program, LS-DYNA is utilized in this study to provide numerical simulations of the dynamic response and residual axial capacity of reinforced concrete (RC) columns subjected to blast loads. Field tests using near-field explosive charge were conducted on two RC column specimens. The test results were compared with the analytical results to validate the finite element model. An extensive parametric study was conducted to investigate the relationship between residual axial capacity and structural and loading parameters such as material strength, column detail and blast conditions. Two empirical equations were derived through a multivariable regression analysis in terms of the various parameters to predict the residual capacity index based on a non-dimensional column dimension parameter (ω_TNT). According to the proposed equations, the residual capacity index can be determined and compared with a service axial load index.     

爆炸冲击作用下连续梁桥动力响应和影响因素研究

运用数值模拟的方法建立爆炸冲击作用下的钢筋混凝土连续梁桥模型,通过改变爆炸作用点位置、爆炸作用比例距离等因素,研究连续梁桥在爆炸冲击荷载作用下的动力响应和敏感性影响因素。结果表明:连续梁桥中跨跨中是其桥面抗爆性能最为薄弱的位置,在抗爆设防中应着重考虑;当装药量相同时,桥梁的破坏程度与比例距离成反比关系;连续箱型桥梁内部爆炸时,对桥梁造成的破坏最为严重,同等条件下下方爆炸时,桥梁破坏程度最小。本研究为桥梁抗爆设计及损伤评估提供理论依据。     

Optimal performance-based design of FRP jackets for seismic retrofit of reinforced concrete frames

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.     

基于纤维模型的钢筋混凝土框架结构爆破倒塌破坏模拟

结构在爆炸荷载下的倒塌破坏模拟日益受到关注.采用基于MSC.MARC有限元软件开发的钢筋混凝土纤维模型程序THUFIBER,对一钢筋混凝土框架结构在爆炸荷载下的倒塌破坏进行了模拟,并根据国家规范特点考虑了框架的正截面和斜截面破坏.计算结果表明,THUFIBER程序可以较好地模拟钢筋混凝土框架结构的倒塌破坏,并对一些关键模型参数进行了讨论.     

A Novel Strain Sensor for Reinforced Concrete Structures

Abstract:  Reinforced concrete (RC) is the most commonly used structural material in civil engineering applications. RC structures have long-term service lives under normal loading conditions; however, overload caused by misuse or statistically remote events such as earthquakes may create damages that, if not detected in time, may eventually cause failure. Hence, it is important to monitor RC structures to take necessary precautions and save human lives. A long-gauge strain (LGS) sensor has been developed to monitor these structures. While it has been developed mainly with concrete applications in mind, the new sensor can also be used in a variety of applications, including measuring strains in pipelines, steel structures, and the like. The proposed sensor system has a very low cost compared with the commercially available competing systems. Prototypes of the proposed strain sensors have been built and calibrated. Test results prove the accuracy, repeatability and reliability of the proposed strain sensor. When the LGS sensor was incorporated into a concrete beam there was very good agreement between the experimental measurement of strain using the LGS sensor when compared with two strain-gauged parallel steel rebars in the same concrete beam.     

Study on Anti-Explosion Behavior of High-Strength Reinforced Concrete Beam Under Blast Loading

Strength of Materials - To investigate the anti-explosion behavior of high-strength reinforced concrete (RC) beam subjected to blast load, the ANSYS/LS-DYNA finite element analysis software was...     

高强钢丝绳网片-聚合物砂浆加固RC板抗爆性能试验研究

为了研究高强钢丝绳网片-聚合物砂浆对钢筋混凝土(RC)板的抗爆加固效果,对5块加固RC板和1块未加固RC板进行了野外现场爆炸试验,研究了砂浆强度、钢丝绳间距、钢丝绳预应力和界面增设销钉等因素对试件的破坏形态、裂缝分布及发展、跨中位移、钢筋应变等影响规律,并对爆炸试验后的试件进行了剩余承载力试验和爆炸损伤评估.研究表明:...     

Experimental and analytical investigation of reinforced high strength concrete continuous beams strengthened with fiber reinforced polymer

Carbon and glass fiber reinforced polymer (CFRP and GFRP) are two materials suitable for strengthening the reinforced concrete (RC) beams. Although many in situ RC beams are of continuous constructions, there has been very limited research on the behavior of such beams with externally applied FRP laminate. In addition, most design guidelines were developed for simply supported beams with external FRP laminates. This paper presents an experimental program conducted to study the flexural behavior and redistribution in moment of reinforced high strength concrete (RHSC) continuous beams strengthened with CFRP and GFRP sheets. Test results showed that with increasing the number of CFRP sheet layers, the ultimate strength increases, while the ductility, moment redistribution, and ultimate strain of CFRP sheet decrease. Also, by using the GFRP sheet in strengthening the continuous beam reduced loss in ductility and moment redistribution but it did not significantly increase ultimate strength of beam. The moment enhancement ratio of the strengthened continuous beams was significantly higher than the ultimate load enhancement ratio in the same beam. An analytical model for moment–curvature and load capacity are developed and used for the tested continuous beams in current and other similar studies. The stress–strain curves of concrete, steel and FRP were considered as integrity model. Stress–strain model of concrete is extended from Oztekin et al.’s model by modifying the ultimate strain. Also, new parameters of equivalent stress block are obtained for flexural calculation of RHSC beams. Good agreement between experiment and prediction values is achieved.     

Evaluation of size dependent design shear strength of reinforced concrete beams without web reinforcement

Analytical studies on the effect of depth of beam and several parameters on the shear strength of reinforced concrete beams are reported. A large data base available has been segregated and a nonlinear regression analysis (NLRA) has been performed for developing the refined design models for both, the cracking and the ultimate shear strengths of reinforced concrete (RC) beams without web reinforcement. The shear strength of RC beams is size dependent, which needs to be evaluated and incorporated in the appropriate size effect models. The proposed models are functions of compressive strength of concrete, percentage of flexural reinforcement and depth of beam. The structural brittleness of large size beams seems to be severe compared with highly ductile small size beams at a given quantity of flexural reinforcement. The proposed models have been validated with the existing popular models as well as with the design code provisions.     

Experimental study and numerical simulation of the damage mode of a square reinforced concrete slab under close-in explosion

Terrorist attacks using improvised explosive devices on reinforced concrete buildings generate a rapid release of energy in the form of shock waves. Therefore, analyzing the damage mode and damage mechanism of structures for different blast loadings is important. The current study investigates the behavior of one-way square reinforced concrete (RC) slabs subjected to a blast load through experiments and numerical simulations. The experiments are conducted using four 1000 mm × 1000 mm × 40 mm slabs under close-in blast loading. The blast loads are generated by the detonations of 0.2–0.55 kg trinitrotoluene explosive located at a 0.4 m standoff above the slabs. Different damage levels and modes are observed. Numerical simulation studies of the concrete damage under various blast loadings are also conducted. A three-dimensional solid model, including explosive, air, and RC slab with separated concrete and reinforcing bars, is created to simulate the experiments. The sophisticated concrete and reinforcing bar material models, considering the strain rate effects and the appropriate coupling at the air–solid interface, are applied to simulate the dynamic response of RC slab. The erosion technique is adopted to simulate the damage process. Comparison of the numerical results with experimental data shows a favorable agreement. Based on the experimental and numerical results, the damage criteria are established for different levels of damage. With the increase of the explosive charge, the failure mode of RC slab is shown to gradually change from overall flexure to localized punching failure.     

爆炸荷载作用下钢筋混凝土柱损伤FEM分析

采用有限元分析方法,对钢筋混凝土柱在爆炸荷载作用下的损伤程度进行了数值分析和评估,为建筑物抗爆设计和选择防爆安全距离提供一定的参考。采用有限元软件对钢筋混凝土框架柱在外部爆炸荷载作用下的非线性反应特征和损伤程度进行分析,采用一种塑性损伤模型,数值模拟分析时考虑材料的应变率效应。将混凝土框架柱的损伤划分为四个等级,并给出柱的防爆等级与距离的评估图。     

Shear capacity of reinforced concrete members strengthened in shear with FRP by using strut-and-tie models and genetic algorithms

Substantial research has been performed on the shear strengthening of reinforced concrete (RC) beams with externally bonded fibre reinforced polymers (FRP). However, referring to shear, many questions remain opened given the complexity of the failure mechanism of RC structures strengthened in shear with FRP. This paper is concerned with the development of a simple automatic procedure for predicting the shear capacity of RC beams shear strengthened with FRP. The proposed model is based on an extension of the strut-and-tie models used for the shear strength design of RC beams to the case of shear strengthened beams with FRP. By the formulation of an optimization problem solved by using genetic algorithms, the optimal configuration of the strut-and-tie mechanism of an FRP shear strengthened RC beam is determined. Furthermore, unlike the conventional truss approaches, in the optimal configuration, compressive struts are not enforced to be parallel, which represents more consistently the physical reality of the flow of forces. The proposed model is validated against experimental data collected from the existing literature and comparisons with predictions of some design proposals are also performed.     

Analytical model for the torsional response of steel fiber reinforced concrete members under pure torsion

Rausch space truss theory (1925) is the earliest theory to predict the torsional response of RC members subjected to pure torsion. Softened truss theory proposed by Hsu considering the softening effect of concrete fairly estimates the torsional strength of the members under pure torsion. These theories consider the member to be a cracked one, so that the truss action activates. This assumption reduces the initial torsional stiffness of the cross-section. However the model proposed by Hsu considering the softening effect of concrete fairly estimates the ultimate torque carrying capacity of the RC member. Fiber reinforced concrete is a better option in the construction of blast resistant and earthquake resistant structures. Relatively little research has been reported on the analytical studies of SFRC members subjected to pure torsion. Thus in this paper an attempt has been made to develop an analytical model for predicting the torque–twist response of SFRC members subjected to pure torsional loads considering the softening effect of concrete. Experimental validation was also presented in this paper.