Ductility of FRP plated flexural members

The design of reinforced concrete (RC) flexural members such as beams, slabs and columns is intrinsically based on the inherent ductility of the member. In reinforced concrete beams and slabs, ductility is generally achieved by using ‘under-reinforced’ sections and generally governed by the neutral axis depth parameter k_u which requires ultimate failure by concrete crushing at a specified strain ε_c. As the plates of fibre reinforced polymer (FRP) plated RC beams can fracture or debond before the concrete crushes at ε_c, the k_u approach is not directly applicable. Hence, new fundamental approaches and a deeper understanding of ductility are required which are the subjects of this paper.     

华龙国际大厦混合结构构件及节点设计

论述了矩形钢管混凝土柱钢框架、混凝土核心筒结构在江西华龙国际大厦的应用，介绍了矩形钢管混凝土混合结构总体设计、节点大样及构造。     

Nonlinear seismic response analysis of reinforced concrete tube in tube structure

Super-highly reinforced concrete tube in tube structure is a developing structure system of high-rise building. The more reasonable derivation process of the multi-vertical-line-element model stiffness matrix is given.On the premise of pointing out the problems of present multi-spring element model, combined with present multivertical-line-element model for analyzing on shear wall, the model is expanded to spatial one, and the stiffness matrix of which is derived. Combined with hysteretic axial model and hysteretic shear model, it is suitable for columns,wall limbs and beams with all kinds of section form. Some examples are calculated and compared with test results,which shows that the models have relatively good accuracy. On the base of the experimental phenomenon and failure mechanism for tube in tube structure specimen, nonlinear seismic responses analysis program on the basis of the advantaged element model for tube in tube structure is developed. Calculation results are in good agreement with those of the pseudo-dynamic tests and the failure mechanism can be well reflected.     

Van Der Waals Force and Asphalt Concrete Strength and Cracking

Van der Waals force between neutral molecules is employed to characterize the interaction among molecules in asphalt cement. Several important consequences emerge from the consideration. The brittle strength of the asphalt binder is shown to be linked to the well depth of the Van der Waals potential and the mesoscopic cracks present within the asphalt binder. Moreover, the elastic modulus of asphalt binder is analytically related to the potential well depth. The strength of the asphalt concrete (AC) is estimated by considering aggregate surface characteristics and the adhesion strength between asphaltenes or resins and molecules of aggregates. These predictions can help design asphalt concrete pavement. Formulas for predicting the binder strength and the interfacial breaking strength between aggregates and binders are derived. These results are supported by reported data. Furthermore, an analytic expression for the strength of AC is given at temperature below the AC glass transition point.     

Behavior of Composite Unreinforced Masonry–Fiber-Reinforced Polymer Wall Assemblages Under In-Plane Loading

An experimental investigation was conducted to study the in-plane behavior of face shell mortar bedded unreinforced masonry (URM) wall assemblages retrofitted with fiber-reinforced polymer (FRP) laminates. Forty-two URM assemblages were tested under different stress conditions present in masonry shear and infill walls. Tests included prisms loaded in compression with different bed joint orientation (on/off-axis compression), diagonal tension specimens, and specimens loaded under joint shear. The behavior of each specimen type is discussed with emphasis on modes of failure, strength and deformation characteristics. Results showed that the application of FRP laminates on URM has a great influence on strength, postpeak behavior, as well as altering failure modes and maintaining the specimen integrity. The retrofitted specimens reached compressive strength of 1.62–5.64 times that of their unretrofitted counterparts, depending on the bed joint orientation, and joint shear strength increased by eightfold.     

Shear Strengthening of Reinforced Concrete Beams Using Carbon-Fiber-Reinforced Polymer Laminates

Shear failure is catastrophic and occurs usually without advance warning; thus it is desirable that the beam fails in flexure rather than in shear. Many existing reinforced concrete (RC) members are found to be deficient in shear strength and need to be repaired. Externally bonded reinforcement such as carbon-fiber-reinforced polymer (CFRP) provides an excellent solution in these situations. To investigate the shear behavior of RC beams with externally bonded CFRP shear reinforcement, 11 RC beams without steel shear reinforcement were cast at the concrete laboratory of the New Jersey Institute of Technology. After the beams were kept in the curing room for 28?days, carbon-fiber strips and fabrics made by Sika Corp. were applied on both sides of the beams at various orientations with respect to the axis of the beam. All beams were tested on a 979?kN (220?kips) MTS testing machine. Results of the test demonstrate the feasibility of using an externally applied, epoxy-bonded CFRP system to restore or increase the shear capacity of RC beams. The CFRP system can significantly increase the serviceability, ductility, and ultimate shear strength of a concrete beam; thus, restoring beam shear strength by using CFRP is a highly effective technique. An analysis and design method for shear strengthening of externally bonded CFRP has been proposed.     

Control of Corrosion-Induced Damage in Reinforced Concrete Beams Using Carbon Fiber-Reinforced Polymer Laminates

This paper presents the results of an experimental study conducted to investigate the effect of carbon fiber-reinforced polymer (CFRP) confinement on the cracking damage induced by impressed current-accelerated corrosion of reinforced concrete beams. The beams were 254?mm deep by 152?mm wide by 3,200?mm long. Two different corrosion configurations, namely uniform and shear-span corrosion, were investigated in eight specimens at three different degrees of corrosion (5, 10, and 15% theoretical mass loss). Uniform corrosion along the whole length of the beams (3,000?mm) and shear-span corrosion (900?mm from each beam end) were considered. The different degrees of corrosion were induced using an accelerated corrosion technique with an impressed current. Based on the results, it was concluded that CFRP laminate confinement reduces corrosion expansion by up to 70% and slows the rate of corrosion through decreasing the corrosion mass loss by up to 35%.     

Interface Characteristics and Laboratory Constructability Tests of Novel Fiber-Reinforced Polymer/Concrete Piles

Conventional pile materials such as steel, concrete, and timber are prone to deterioration for many reasons. Fiber-reinforced polymer (FRP) concrete composites represent an alternative construction material for deep foundations that can eliminate many of the performance disadvantages of traditional piling materials. However, FRP composites present several difficulties related to constructability, and the lack of design tools for their implementation as a foundation element. This paper describes the results of an experimental study on frictional FRP/dense sand interface characteristics and the constructability of FRP–concrete composite piles. An innovative toe driving technique is developed to install the empty FRP shells in the soil and self-consolidating concrete is subsequently cast in them. The experimental program involves interface shear tests on small FRP samples and uplift load tests on large-scale model piles. Two different FRP pile materials with different roughness and a reference steel pile are examined. Static uplift load tests are conducted on different piles installed in soil samples subjected to different confining pressures in the pressure chamber. The results showed that the interface friction for FRP materials compared favorably with conventional steel material. It was shown that toe driving is suitable for installation of FRP piles in dense soils.     

Prediction of the Failure Time of Glass Fiber Reinforced Plastic Reinforced Concrete Beams under Fire Conditions

A model is proposed to predict the time to failure of reinforced concrete beams in a fire. The model is developed specifically to predict the lifetime of beams reinforced with glass fiber reinforced plastic rebar, but is applicable to beams with any form of reinforcement. The model is based on the calculations for flexural capacity and shear capacity of beams embedded within ACI design codes where time and temperature dependent values for rebar modulus and strength and concrete strength replace the static design values. The base equations are modified to remove safety factors and where necessary the temperature induced reductions in strength for concrete and steel are derived using the equations presented by EUROCODE 2. In order to validate the model it was used to predict the failure times of steel rebar reinforced beams that had been documented in the literature. There was excellent agreement between the model and the reported lifetimes for these conventional beams. The model was applied to predict the lifetimes of two beams that had been manufactured and tested for destruction in a fire by the research group. The model predicted that the failure mode of the beams would be because of rebar rupture as opposed to the design condition of concrete crushing and this was confirmed by the experimental test results. The model provided reasonable agreement with experimental results with a lifetime of 108?min predicted based on flexural failure and 94 and 128?min observed in the experiments.     

Experimental Investigation of Nonconventional Confinement for Concrete Using FRP

The present study investigates experimentally the behavior of concrete confined with fiber reinforced polymers (FRP) in the form of jackets which are applied according to a number of nonconventional techniques. First, the effectiveness of various jacketing configurations combined with anchors as a measure of increasing the strength and deformability of L-shaped columns is investigated. It is concluded that easy to install and low-cost anchors made of resin impregnated fibers properly placed at the reentrant corner of L-shaped columns enable excellent mobilization of confining stresses supplied by the FRP jackets. Next, a number of alternative confinement methods are investigated on concrete cylinders, aimed at quantifying the effectiveness of (1) unbonded jacketing, (2) spirally applied strips attached only at their ends, and (3) jacketing directly on concrete with mortar plastering. Although the study may be regarded as preliminary, it provides useful experimental support to a number of techniques which have the potential to open new horizons in the field of externally applied FRP for enhancing concrete confinement.