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Although a limited number of studies have been conducted on the use of externally bonded composites for torsional retrofit or strengthening of reinforced concrete (RC) members, very few are available on torsional repair. This paper evaluates a method for repairing severely damaged RC columns subjected to torsional moment using externally bonded carbon fiber-reinforced polymer (CFRP) composites. A half-scale RC column that was previously tested to failure under constant axial load and cyclic torsional moment was repaired with externally bonded CFRP using a rapid methodology. CFRP sheets with fibers oriented in both the transverse and longitudinal directions were applied to restore the strength and ductility of the damaged column to its original condition. This study demonstrates that this method can be used to restore the torsional performance of severely damaged RC columns. Contributions of the transverse and longitudinal CFRP sheets to the torsional resistance are evaluated, and repair design for torsional moment using this method is discussed. [ABSTRACT FROM AUTHOR]

The vertical load distribution between the walls in a masonry building is a difficult issue in structural engineering. The absence of research regarding this subject results in using simple load distribution methods by the designers. This paper presents a study of the vertical load distribution between the walls in a full-scale four-story masonry building. Ninety blocks of a four-story building were instrumented with strain gauges and their behaviors were evaluated after an external loading was applied on some slabs. The distribution of the vertical loads in this building is also evaluated using a simple theoretical design model widely used in structural design practice. Experimental results exhibited vertical load redistribution between the walls and high influence of the flexure of slabs and walls on this distribution. Comparing experimental and theoretical results, there was similarity between the experimental and numerical results inside some wall groups, although the simple design model produced divergent stress values in the presence of significant flexural effects. [ABSTRACT FROM AUTHOR]

This study provides analytical solutions of elastic stress distributions in simply supported deep beams through translucent loadpath modeling. The load-path model is established with graphical and analytical features, which aides in the visualization and quantification of the flow of internal forces within deep beams. Nonlinear strain distributions in deep beams originate from the spread of localized forces within the beams, and this effect can be represented by a beam system subjected to compressions at opposite corners. Explicit expressions for transverse stresses and resultant tensions are obtained for deep beams subjected to various loading patterns using the principle of superimposition. The estimation of resultant tensions using the method presented is practical in the serviceability design of deep beams (particularly for very deep beams with depths greater than their spans), and can serve as a quantitative basis in developing strut-and-tie models. [ABSTRACT FROM AUTHOR]

In this paper, a novel bond-slip-strain relationship for a strand in the transfer zone of a pretensioned concrete member is presented. To draw a relationship among the bond stress, strand strain, and slip along the transfer zone, pretensioned, prestressed concrete members were fabricated, and strand strains were measured from electrical resistance steel gauges attached on the strand during prestressing force release. The test variables were the compressive strength of the concrete, the size of the cross section, the cover thickness, the diameter of the strand, the curing method, and the debonded region. Estimates obtained from the proposed model were in good agreement with the test results from other studies, as well as those from this work. Using the advantage of the strain term in the proposed formulation, the applicability of the derived model to fiber-reinforced polymer tendons was also evaluated. [ABSTRACT FROM AUTHOR]

Proposed is a realistic estimation and appropriate prediction equation for transfer length in pretensioned, prestressed concrete members. The purpose of this paper is to explore the important factors that affect the transfer length and then to propose a realistic equation for transfer length in pretensioned concrete members. For this purpose, several series of tests have been conducted to measure the transfer lengths in pretensioned members. Finite element analyses have been also conducted to obtain the transfer length. An appropriate bond stress-slip relation between prestressing steel and concrete was derived, then employed in the finite element analysis. The present study indicates that the compressive strength and concrete cover are also very important parameters in transfer length in addition to the prestress magnitude and strand diameter. A realistic prediction equation for transfer length was therefore proposed in this study for more rational design of pretensioned concrete members. [ABSTRACT FROM AUTHOR]

An evaluation procedure for predicting the unbonded tendon stress in the continuous post-tensioned beams was performed and calibrated through analyzing experimental data from 16 two-span specimens under static loading up to failure. As the relationship between the increase of the tendon stresses and the change of the tensile nonprestressed reinforcement stresses in a same critical section of a post-tensioned beam, response is nearly linear at various levels of loading such as zero, elasticity, cracking, and before yield of nonprestressed tension reinforcement. The non-prestressing bonded steel satisfied strain compatibility. Thus, the increase of the tendon stresses at the service load may be determined through linearly reducing the change of the tensile steel stresses. A model for predicting the ultimate stress of unbonded tendons treats the prestressing reinforcement index and the global reinforcement index as the two independent variables. This and the other variables, including the ratio of the two global reinforcement indexes of support and midspan, and span-depth, affect the rotation capacity of plastic hinges. This prediction model was derived from the equilibrium of the ultimate flexural capacity, and was calibrated by current testing data. Compared with the ACI code and China specification, the proposed equation of the model was validated and was found to provide better accuracy for predicting the ultimate stress of the unbonded tendons in the continuous posttensioned beams. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of the stress and deflections changes due to creep in statically determinate composite steel-concrete beams. The mathematical model involves the equation of equilibrium, compatibility, and constitutive relationship, that is, an elastic law for the steel part and an integral-type creep law of Boltzmann-Volterra for the concrete part. Based on the theory of the viscoelastic body of Arutyunian-Trost-Bažant for determining the redistribution of stresses in beam sections between a concrete plate and steel beam with respect to time t, two independent Volterra integral equations of the second kind have been derived. A numerical method based on linear approximation of the singular kernal function in the integral equation is presented. An example with the proposed model is investigated. The creep functions are suggested by the Gardner and Lockman model. The elastic modulus of concrete Ec(t) is assumed to be constant in time t. [ABSTRACT FROM AUTHOR]

An experimental study was performed to evaluate the applicability of ACI 318 to the Class B splice of 600 MPa (87 ksi) reinforcing bars. Twelve simply supported beams and slabs with reinforcing bar splices were tested under monotonic loading. The test parameters were the reinforcing bar diameter, concrete cover thickness, concrete strength, and stirrup spacing. Concrete strengths ranged from 24.7 to 55.3 MPa (3582 to 8021 psi). Most of the specimens were designed to satisfy the Class B splice length specified by ACI 318. The average bar stresses resulting from this test were compared with the predictions by the ACI 318 provisions. The results showed that the reinforcing bar splices gave a satisfactory performance for all D13 (diameter = 13 mm [0.51 in.]) bar splices. For D22 and D32 bars, the use of either transverse reinforcement or thick concrete cover was recommended to develop the specified yield strength of 600 MPa (87 ksi). The test results were also compared with the predictions by the ACI 408R-03 and Eurocode 2 provisions. [ABSTRACT FROM AUTHOR]

In this study, a generalized equivalent Stress Block Model has been proposed that is applicable to all types of concrete, including lightweight and high-strength concrete (HSC). First, available stress-strain models for concrete were verified through an extensive database. Then, the coefficients used in the proposed stress blocks were formulated based on a nonlinear regression analysis of the values determined from the layer-by-layer integral evaluation approach. The hypothesis underlying this integral approach is that the magnitude and location of the resultant force in the equivalent stress distribution are the same as those in the actual distribution. The extreme compressive fiber strain of 0.003 and the factor of 0.85 used to compensate for the difference between the in-place strength and the cylinder strength were assumed, as was done for normalweight and/or normal-strength concrete (NSC). The reliability and safety of the proposed stress blocks were confirmed through comparisons with the flexural capacities measured from approximately 175 normalweight and 80 lightweight concrete (LWC) beams, and approximately 100 normalweight concrete (NWC) columns. [ABSTRACT FROM AUTHOR]

The article presents a discussion on the paper "Determining Slipping Stress of Prestressing Strands in Confined Sections," by Mohamed K. ElBatanouny and Paul H. Ziehl. The discusser ask the authors as to how they obtained the transfer lengths when the data could not be found in the paper authored by Mohsen Shahawy and Moussa Issa. According to the discusser, environmental studies on development length and bond behavior after strand slippage have been conducted using the ECADA test method.

The article responds to comments on a paper about the transfer length in prestressed self-consolidating concrete (SCC) box and I-girders. It notes the elimination of conventional concrete (CC) load-slip curves mainly because of paper length's constraints. It agrees on the increase in time strain due to concrete shrinkage and creep.