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Lateral collapses due to earthquakes and progressive collapses due to the sudden destruction of the columns are two of the most commonly encountered failure mechanisms for buildings. To simultaneously improve the seismic performance and the progressive collapse resistance of reinforced concrete (RC) frame structures, this paper presents a novel method using kinked rebar. Kinked rebar has a large deformability because it can be gradually straightened under a tension force, and it can be placed near the inflection points in beams under uniform vertical loads in RC frame structures. First, uniaxial tensile tests were performed to study the equivalent stress-equivalent strain relation and the deformation mode of the kinked rebar. Second, three-point and four-point bending tests were performed to investigate the load-deflection relationship and the failure modes of simply supported beams with local kinked rebar. Third, numerical simulations based on the fiber beam model were conducted to study the seismic behavior and progressive collapse resistance performance of a six-story RC frame with local kinked rebar in the beams. The mechanical behavior of the new beam section with kinked rebar was used to relocate the plastic hinges and to successfully improve the calculated progressive collapse resistance of the RC frame.
Based on the bending-active concept, this paper presents a self-shaping system with bunched carbon fiber-reinforced polymer (CFRP) rods to construct complex curved surfaces, establishing an overall design and construction process. Such component consists of a bunch of slender and easily bendable CFRP rods that are preformed and then bounded by connecting joints. Then, those components form free-form spatial structures. The proposed system offers several advantages: strong designability, low transportation cost, short construction period, polished appearance and low maintenance requirements during service. For component design, to determine the shape of such component, a two-stage mechanical analysis is proposed based on the large deformation theory and finite element analysis (FEA): a form-finding process to determine the deformed component shape through its cross-sections and boundary-load conditions; and a reverse form-finding process to obtain these above-mentioned parameters from a given component shape. The reliability of both methods is verified through in-plane bending tests. A design demonstration of a saddle-shaped curved spatial structure is performed using this method. Overall, the proposed system can guide the actual construction projects of complex curved surfaces with self-shaping bunched CFRP rods.
This paper presents a design and construction schemes of a pipe jacking project in Kunming, China in detail. The underpass, having a width of 6.9 m and a height of 4.9 m, was jacked 46m in water-filled clay under a busy viaduct with 4.5 m overburden soil., Some adjustments have been made to the construction process due to the characteristics of the soil layer, the surrounding environment and the existing pipeline. During the whole construction process: the pipe jacking passes through the shallow confined aquifer with high water content and high void ratio, it is easy to produce rheology. In addition, the attitude control of whole tube is also a difficulty, and some adjustments have been made to this problem; the monitoring scheme has also been adjusted accordingly. In general, this project is completed successfully and the traffic on ground and viaduct runs well during the whole construction process.
Adhesive bonding has gained increasing acceptance in joining pultruded glass fiber reinforced polymer (GFRP) sections. However, one of the major issues hindering the widespread application of adhesive bonding in building and construction industries is the difficulty in predicting the mechanical behavior of the joints in the presence of adhesion defects. This paper investigates the damage tolerance of the adhesively bonded pultruded GFRP double-strap joints under quasi-static tensile loading using finite element analysis. Defects of various locations (along the bond length), sizes, and numbers were embedded within the bondline. A two-dimensional (2D) stress analysis was conducted to assess the effects of the bondline defects on the out-of-plane displacement, stress distribution, and peak stresses of the joints. Three-dimensional (3D) progressive damage models were further developed to predict residual joint capacity and provide insights into the effects of the adhesion defects on the damage mechanism of the joints. The progressive damage model uses the cohesive zone model (CZM) to simulate progressive interlaminar damage within the adherends as well as adhesive-FRP interface debonding. The proposed FE model was validated with published experimental data, and an excellent correlation was found between experimental and numerical results. The validated model was then used in a parametric study to assess the effects of design parameters such as adhesive types (from highly brittle to highly ductile) and joint geometry (adhesive chamfering, adherend chamfering, and recessing) on the damage tolerance of adhesively bonded joints. This paper also reports a comparative study on the damage tolerance between GFRP double-strap, single-strap, and single-step joints. The stress analysis results revealed that the presence of the bondline defects could increase the out-of-plane displacement of the adherends and the peak shear and peel stresses at the overlap ends. High-stress concentrations were also observed in regions adjacent to the defect extremities. The double-strap joints exhibited better damage tolerance than the single-strap and single-step lap joints. The damage tolerance of the joints can be improved by using stress-reduction methods such as adhesive chamfering, adherend chamfering, and recessing.
It is prerequisite to investigate the contact characteristics if enough simulation accuracy is needed for the prediction of the mechanical system, but the contact contributes the major deformations of the whole system and give rise to the discontinuity. This paper presented a method on how to model and simulate the contact process based on the finite element method. In order to explore contact performance under the external force, a modeling method was studied based on the permeation method. The permeation method was proposed for the description of contact, and the permeation was determined by the contact stiffness and the external load. Moreover, both the normal and tangential permeations were involved for the study of two orthogonal directions. Additionally, a case study of plane-plane contact with a typical material constitutive model was presented. Results showed that the permeation method was efficient for the study of the structure analysis. And the compensation of the displacement adjusted the difference of the displacements to simulate the contact process because of the permeation.
Novel hybrid members, namely, CFRP-Al hybrid tubes, which are composed of Al (aluminum alloy) and CFRP (carbon-fiber-reinforced polymer) jackets, represent promising axial load members in civil engineering. Long CFRP-Al hybrid tubes with circular and square hollow sections are investigated in this study using bending and axial compressive buckling tests. Compression buckling analysis is performed using finite element analysis (FEA) and section analysis, which allow one to better understand the unique “partial elastic buckling” behavior of long hybrid members. In addition, a good agreement between FEA and bucking test results is achieved. Finally, based on FEA and the traditional Perry-Robertson formula, the column curves for long CFRP-Al hybrid tubes are given for design.
This paper uses a glass fiber reinforced polymer(GFRP) tube to strengthen an axial compressing angle steel component to avoid buckling. The axial compression experiments of nine specimens have been carried out for investigating the factors of three slenderness ratio and two kinds of reinforced structure forms. The experimental study show that the anti-buckling strengthening method has good operability. The GFRP tube buckling strengthening method improves the buckling capacity for compression angle steel members. The ductility of strengthened angle steel components is improved and the ultimate bearing capacity increases by 6.16% ~ 37.58%; the method of slenderness larger component reinforcement effect is obvious, and the failure mode must be changed. The results calculated by revised formulas for GFRP tube stiffness contribution coefficients proposed are in a good agreement with the test results.
A novel assembly FRP (fiber-reinforced polymer)-concrete hybrid beams/decks system is proposed and investigated in this paper. The performance of FRP shear key (SK) connector, FRP stay-in-place (SIP) form, and their combination for the FRP-concrete hybrid beams/decks is evaluated. The slip modulus and interfacial shear capacity of SK, SIP and their combination were investigated via push shear tests with thirteen specimens and four-point bending test with three FRP-concrete hybrid beams. Push-out test results showed that SK has the same shear capacity level and about ten times the slip modulus compared with steel bolt (SB). The cross section of SK is not a significant parameter because all of the shapes can enhance nearly full composite action between the FRP girder and concrete block. SIP can supply a strong initial natural bond with concrete and substantially save the form for concrete casting. This connection-form system combines the SB, SK and SIP as a structurally optimized design of shear connection and the permanent form. The beam test revealed that this connection system supplied full composite action till the failure of the FRP girder. Deflection of the FRP-concrete beam with the novel system can be predicted using equations based on the full-composite action assumption.
The design of FRP profile-concrete composite sections, including beams and decks, is usually governed by the shear strength of the FRP profiles. However, analytical methods that can precisely predict the shear capacity of the composite sections have not been well developed, because there is lack of knowledge of the FRP-concrete composite action and distribution of shear stress along the FRP. This paper investigates the shear behaviors of FRP-concrete composite sections and develops formulae to predict the shear capacity of the composite sections. First, flexural tests of three FRP-concrete composite beams were conducted to investigate the shear failure mode and interface behaviors. All the beams failed in FRP shear fracture along horizontal direction. Then, push-out tests were used to determine the slip property for the FRP-concrete interface which reveals that FRP stay-in-place form and steel bolts can ensure full and partial composite action, respectively. Based on the experimental study, closed-form equations to compute the maximum shear stress are derived and validated against experimental data in this paper and literature. Finally, simple yet reliable equations of shear capacity are derived and recommended for engineers to design the FRP-concrete composite sections.
A novel method for obtaining initial geometric imperfections by three-dimensional (3D) laser scanning is developed to study a discovery of reducing initial geometric imperfections using pre-stressed (PS) carbon fiber reinforced polymer (CFRP) strips. New methodologies for establishing digital geometric models of specimens based on point cloud data are presented. The initial deflections along the weak axes of two series of specimens with I-shaped section, 10 specimens in total, are obtained by these methods. It is found that the initial deflections along the weak axes of the steel columns are reduced by the PS CFRPs. Then, the force method is implemented to establish a theoretical model for steel columns strengthened with PS CFRPs. The model illustrates the mechanism for decreasing geometric imperfections in a self-balanced process. Corresponding equations based on the theoretical model are proposed to explain the reduction of the initial deflections. Finally, the model is verified by comparing its predictions to the measurement results.
目的 探讨公交车爆炸伤伤员的伤情特点及急救和治疗方法.方法 回顾分析二起公交车爆炸伤87例伤员的伤情特点和处理方法.结果 本组87例伤员,9人当场炸死,3人后送途中死亡,18人门诊观察数日回家,57人住院治疗,其中除2例3肢骨缺损行二期植骨术,2例胫神经损伤二期行神经修复术外,其余病人均痊愈出院.结论 爆炸伤病人伤情重且复杂,多为复合伤,死亡率高,接收成批伤员,应做好院前抢救和分类工作,分轻重缓急安排好抢救、治疗及手术.
Externally bonded fibre-reinforced polymer (FRP) composites can be applied to strengthen and repair existing steel structures. In order to understand and quantify the behaviour of the bonded interface, researchers have conveniently tested FRP-to-steel joint assemblages. Both single- and double-shear joints of varying boundary conditions have been tested to date in which either the steel or FRP components have been loaded. In addition, the material and geometric properties of the joint materials have been varied and such variation in properties and test configuration will cause variation in the distribution and magnitude of interfacial stresses. This study presents the results of finite element simulations of the interfacial stresses of several FRP-to-steel joint configurations considered by researchers to date. Numerical simulations of interfacial stresses are also conducted on an FRP-strengthened I-beam and several key locations are examined in greater detail such as at the plate end, an intermediate fatigue induced crack, and a yielded zone. The beam stresses are compared with the stresses from the joint models and then joint configurations are identified which best capture the interfacial stress distributions at various positions along the length of the beam.
