Punching Shear Strength of Reinforced Concrete Flat Plates with Openings

Test results of six half-scale reinforced concrete flat plates connections with an opening in the vicinity of the column are reported. The test specimens represent a portion of a slab bounded by the lines of contraflexure around the column. The tests were designed to study the effect of openings on the punching shear behavior of the slab-column connections. The test parameters were the location and the size of the openings. One specimen had no opening and the remaining five had various arrangements of openings around the column. All specimens were cast with normal density concrete of approximately 30 MPa compressive strength. The openings in the specimens were square, with the sides parallel to the sides of the column. Three sizes of openings were used: the same size as the column (150 x 150 mm), 67 percent of the column size (100 x 100mm), and 150 percent of the column size (225×225mm). Due to the presence of the openings, the specimens showed a decrease in punching shear capacity ranged between 11.43% and 29.25% with respect to the control solid slab. Also, the stiffness decreased between 0.31% and 83.00%, depending on the size and location of these openings with respect to the column

ANALYSIS OF CONCRETE FLEXURAL MEMBERS REINFORCED WITH FIBRE POLYMER

Analytical model is used in this paper to predict the load carrying capacity of structural concrete members under flexural and normal force which can be concentric or eccentric. The analysis is based on requirement of equilibrium and compatibility of strain in concrete and steel or FRP. The adopted model is based on the real stress strain diagrams for materials. In accordance with this model, the member cross section is covered by a mesh with the smallest cells. After that, stress or strain is determined in each cell and the integral is substituted by the process of summation to define the elements of stiffness matrix. The force vectors equations have nonlinear behaviour. However, in this model, these nonlinear equations are changed to linear equations using the iteration methods with fixity of secant modulus of elasticity in each iteration cycle. In this paper. FORTRAN computer program language is used to compute the force and strains vectors. The comparison between the analytical resaks obtained from the used model and experimental data for other researchers is performed. The analytical model is giving a reasonable agreement between the theoretical and experimental results

SHORT TERM DEFLECTION OF ORDINARY, PARTIALLY PRESTRESSED AND GFRP BARS REINFORCED CONCRETE BEAMS

The behavior of structural concrete beams is studied under short-term loading. A computer program developed originally by Oukaili to evaluate curvature is modified to evaluate the deflection for flexural structural concrete members. The program deals with actual stress-strain relationships of concrete and steel. The analysis is based on requirements of equilibrium and compatibility of strain in concrete and reinforcement. The proposed model is used in conjunction with the step by step analysis for small loading increments that allows the determination of the history of strain and stress in concrete with prestressing steel or non-prestressing reinforcement only or prestressing and non-prestressing reinforcement together. The evaluation of curvatures for the structural member involves iterations for computing the strains vectors at each analysis step. Newmark's numerical integration is used to evaluate the deflection of the member depending on the curvature values. The stress-strain model that was proposed by (Korpenko et al. 1986) is used and compared with experimental data and other analytical models for each of concrete and steel. The comparison showed good agreement between the model used and the experimental data. This relationship is used in SECTION program and presented in this study. The analytical results for load-deflection diagram are compared with available experimental data. The comparison has shown good agreement

Strengthening and Closing Cracks for Existing Reinforced Concrete Girders Using Externally Post-Tensioned Tendons

This research is devoted to study the strengthening technique for the existing reinforced concrete beams using external post-tensioning. An analytical methodology is proposed to predict the value of the effective prestress force for the external tendons required to close cracks in existing beams. The external prestressing force required to close cracks in existing members is only a part from the total strengthening force. A computer program created by Oukaili (1997) and developed by Alhawwassi (2008) to evaluate curvature and deflection for reinforced concrete beams or internally prestressed concrete beams is modified to evaluate the deflection and the stress of the external tendons for the externally strengthened beams using Matlab 7.0. The analytical investigation is implemented on three ideal reinforced concrete beam models, each model is considered to be strengthened using three types of external tendon profile (straight, draped and double draped), where each type of tendon profile is analyzed separately. No comparisons were made with analytical or experimental investigations, because no publications for this kind of studies were found

EFFECT OF PRESTRESSING FORCE ONTORSION RESISTANCE OF CONCRETE BEAMS

This study presents an experimental and theoretical investigation of torsion behavior of prestressed concrete rectangular beams without ordinary (or typical) reinforcement. Two concrete beams with concentric prestressing tendons (6-strands of 7 wires) and two plain concrete beams were tested in this investigation with f'c= 44MPa was used. Experimental results showed that the ultimate torsional strengths increased by about 70% for the tested beams containing concentric prestressed strands over the plain concrete beams. Also the angle of twist decreased (68.8%).Crack patterns and the effect of compressive force due to prestressing tendons and high strength concrete can be denoted from the helical mode of single crack at midspan of the beams under testing and from the sudden failure mode. In the analytical work P3DNFEA (Program, three-dimensional nonlinear finite element analysis), by Al-Shaarbaf has been utilized. Three dimensional nonlinear quadratic 20 -node brick elements were used to model the concrete, while, the prestressing strands were modeled by embedded representation. Reinforcing bars (Prestressing strands) were assumed to be capable of transmitting axial forces only. It was found that the general behavior of the finite element showed good agreement with observations and results from the experimental tests

The Use of Bracing Dampers in Steel Buildings under Seismic Loading

This study focuses on the modeling of manufactured damper when used in steel buildings. The main aim of the manufactured dampers is to protect the steel buildings from the damaging effects that may result due to earthquakes by introducing an extra damping in addition to the traditional damping. Only Pure Manufactured Dampers, has been considered in this study. Viscous modeling of damping is generally preferred in structural engineering as it leads to a linear model then it has been used during this study to simulate the behavior of the Pure Manufactured Damper. After definition of structural parameters of a manufactured damper (its stiffness and its damping) it can be used as a structural element that can be added to a mathematical model of the structure. As the damping of manufactured dampers is generally greater than the damping of traditional materials, then the resulting damping matrix for the whole structure will be classified as a nonclassical damping. As most of literature on earthquake engineering have been written in terms of terminology related to mode superposition method and as this method is applicable to classical damping only. Then, this study tried to check the accuracy of the mode superposition method when applied to a structure with manufactured dampers. In this checking, approximated results of mode superposition method have been compared with more accurate results of direct integration method. From this comparison, it has been noted that the mode superposition method has different levels of accuracy depending on the relation between the fundamental frequency of the structure and the dominate frequency of the earthmotion. If the frequency of the structure is approaching to a dominate frequency of the earthmotion, then the damping effect will be important and the difference between the direct integration method and the model superposition method is increasing and vice vers

NONLINEAR ANALYSIS OF CFRP- PRESTRESSED CONCRETE BEAMS SUBJECTED TO INCREMENTAL STATIC LOADING BY FINITE ELEMENTS

<p>In this work a program is developed to carry out the nonlinear analysis (material nonlinearity) of prestressed concrete beams using tendons of carbon fiber reinforced polymer (CFRP) instead of steel. The properties of this material include high strength, light weight, and insusceptibility to corrosion and magnetism. This material is still under investigation, therefore it needs continuous work to make it beneficial in concrete design. Four beams which are tested experimentally by Yan et al. are examined by the developed computer program to reach a certain analytical approach of the design and analysis of such beams because there is no available restrictions or recommendations covering this material in the codes. The program uses the finite element analysis by dividing the beams into isoparametric 20-noded brick elements. The results obtained are good in comparison with experimental results.</p

Response of reinforced concrete beams with multiple web openings to static load

Web openings in beams occur quite often in practice to provide convenient passage of electrical and mechanical ducts. Shear failure may dominate in cases where web opening created or the flexural strength has been increased. In such cases, increasing the shear capacity can prevent catastrophic shear failure. In this paper, the investigation of the response of simply supported reinforced concrete T-beams with multiple web circular openings is presented. An experimental research program was conducted on the shear behavior of simply supported beams subjected to an incremental concentrated static load at mid span. Seven reinforced concrete T-beams were tested with two design parameters, including number of web circular openings (four or six) and the method which was used to strengthen the member at openings (using internal deformed steel bars as in the case of the openings are planned before casting the beams or using carbon fiber reinforced polymer (CFRP) fabric as in the case of the openings will be created in the existing beams). Test results indicated that the strengthening of beams at openings may compensate the decrease of the beam capacity due to the existence of the openings under static loading. The compensation of the beam capacity depends on the strengthening method which was adopted. The gain in shear capacity of the tested beams ranged between 27% and 92% which also represents about 86% to 114% of the reference solid beam capacity under static loading. A nonlinear finite element program, ANSYS 12.1 release, was used to validate the results of the tested beams. Comparisons between the finite element predictions and experimental results in terms of failure loads and load-deflection relationships are presented and showed good agreement

Flexural behavior and sustainable analysis of polymer bubbuled reinforced concrete slabs

This work presents the flexural capacities and sustainable analysis of reinforced concrete (RC) two way hollow slabs with polymer sphere voids, also known as polymer bubbled RC slab system. A polymer bubbled RC slab has two-dimensional arrangement of voids included to reduce the self-weight. The strength and behavior of bubbled RC slabs with polymer spheres voids is investigated experimentally. Eleven RC square slabs of 1000mm x 1000mm dimensions have been tested to obtain the flexural behavior. Variables of the experimental work are: diameter of polymer spheres, thickness of reinforced concrete slabs, and percentage of Metakaolin (cement replacement). It has been found that bubbled RC slab, (with ratio of bubble diameter B to slab thickness H, B/H=0.51 to 0.80), has about (90 to 100%) of the ultimate load capacity of a similar reference solid slab (which has the same slab thickness). Also, bubbled slabs consume about (70 to 75%) of the concrete needed for the similar solid slab. An increase in the deflection at 0.7