Transverse opening in a reinforcedconcrete beam allows the crossing of mechanical and electrical services through the beam. However, it affects the strength of a beam. Understanding its structural behaviour is crucial to ensure a safe design of the beam. For that, an experimental study was carried out on reinforcedconcretebeams with circulartransverseopenings. The four-point load test was conducted to study the effects of the size and the position of the opening on the beam performance under the shear and flexural loads. In addition, three reinforcing methods for the opening were tested. The beams were evaluated in terms of the load-displacement responses, mechanical properties, deflections, and failure modes. The opening with the diameter not exceeding 0.25 times beam height affected about 20% of beam strength (without reinforcements at the opening). The diagonal bar reinforcing method effectively restored the beam strength for the opening size not exceeding 1/3 of beam height. The equation model proposed conservatively predicted the ultimate capacity of the beam with a transverse opening.
Spandrel beams are very command members in many building frames. Such members are subjected to twisting about its longitudinal axial, known as torsion, in addition to the shearing force and bending moment; hence the external loads act far away from the vertical plane of bending. Torsion may be classified in to two main types  : the first type is called equilibrium or statically determinate torsion at which the torsional moment cannot be reduced by the redistribution of internal forces. It develops when the external load has no alternative load path but must be supported by torsion. For such cases, the torsion required to maintain static equilibrium and prevent collapse of the structure. Figure 1(a) shows an example of torsion to maintain equilibrium on bridge deck. The second type is called compatibility or statically indeterminate torsion in which torsional moment can be reduced by redistribution of internal forces generated by twisting. This type generates in primary structures beams supporting secondary beams for example, the torsion developed in to spandrel beams of a building caused by loading from a cast in place slab, and equal to the negative moment in the slab. Figure 1 (b) shows the torsion due to rotation. In this type, the torsional stiffness of the spandrel beam must be considered. This loading mechanism develops torsional forces that are transferred to columns.
ABSTRACT - In modern building construction, utility ducts and pipes are accommodated in the space above the false ceiling. There will be high stress concentration around the openings due to the implementation of transverse opening in the web. These results in reduction in beam stiffness. Therefore, while providing large openings, the behaviour of the beam must be properly accounted. Most of the cases the conventional concrete cannot completely fill the congested reinforcement around the opening. Hence Self-compacting concrete (SCC) can be used in these beams, as it can easily fill those congested reinforcement without any vibration. It also prevents the local cracks around openings. The use of fibres extends its possibilities.
All the specimens were white washed in order to facilitate marking of cracks. The GPC beam specimen was kept under loading frame with simply supported conditions at both ends. The beam was simply supported on the reaction blocks by a hinged plate at one end and roller plate at the other end. A 2000kN servo-controlled hydraulic actuator was used to apply the monotonic loadings. All specimens are tested using two point loading with shear span to effective depth ratio of 1.5 and 2. The displacement control mode has been conducted on both the test specimens. The tests are carried out at the FFL, CSIR-SERC. Figure 1 shows the details of the test setup. LVDTs are located at three places, one at mid span and two under load points. LVDTs are also used for each test to monitor shear strain of GPC and OPCC beams. Electrical strain gauges are used in the test, strain gauges are used on the surface of the longitudinal steel reinforcement and transverse steel. All the test specimens are tested increment loadings. After applying each increment of load, load, deflection and strain are measured simultaneously. Loading increment is continued in increments up to the failure of the specimen. The behavior of the beam was observed carefully and the crack widths were measured using a hand held microscope. All the measurements including deflections, strain values and crack widths were recorded at regular intervals of load until the beam failed. Figure 2 shows the typical crack-pattern in RPCC and RGPC beams. It was observed that flexural failure mode for RGPC and RPCC beams.
This research presents the flexural behavior on reinforcedconcrete beam with transverse web opening constructed from layered concrete. The layered concrete combining normal concrete and lightweight aggregate concrete (LWC) are depended in present study. In the experimental program, 13 models of normal and layered reinforcedconcretebeams are tested under the effect of four-point loads. All beams had the same overall geometrical dimensions and main longitudinal top and bottom with internal diagonal reinforcement provided around the openings. One of the beam specimen is tested as control beam and the other specimens are divided into three groups [G1, G2, and G3] to study the effects of the following variables: effect of presence of web openings, layered system, lightweight aggregate (partially volumetric replacement of normal aggregate by thermostone) on the ultimate load, cracking load, cracking pattern and energy absorption capacity. The existing of an opening in beam specimens reduced the flexural capacity of beams with a percentage depending on the size of opening and opening number. The test data obtained from the adopted layered technique of (NEW) and (LWC) have shown that for beams constructed from two layered concrete (LWC with thermostone in the web and bottom flange of I-beam section) ultimate load is decreased about (9.3%-48.8%). It has also, the beams constructed from three-layered of concrete (LWC with thermostone in the web of I-beam section), their ultimate load is decreased about (25.6%-58.1%). On the other hand, magnitude increased of energy absorption capacity are achieved by the decreased opening size, introducing the full size opening of dimension (100×1000) mm reduces the energy absorption capacity of the RC I-section beams at least 80% compared to solid beam while the beam with opening size (100×100) mm decrease up to 16%. In the case of the layered concretebeams specimen, the real influence of lightweight concrete (LWC) type in the layered reinforcedconcrete is observed significantly after increasing the length of opening more than 100 mm.
Although these findings agree with the hypothesis proposed by Dladla (2014), that increased corrosion damage length is likely to reduce the moment capacity of RC beams, they are also in stark contrast with the findings presented by Dladla (2014). His research revealed an increase in flexural capacity with increasing damage length. The FEM study by Mundeli (2014) which ran concurrently with the one carried out by Dladla (2014) also reported an increase in load carrying capacity with an increase in damage length. One very notable difference between this study and the ones carried out by Dladla (2014) and Mundeli (2014) is the actual degree of corrosion. Dladla (2014) made use of simulated corrosion which yields a perfect uniform degree of corrosion by grinding off a portion of the steel cross- section. Mundeli (2014) also modelled uniform corrosion in his study. In this study accelerated corrosion was used, which does not yield perfectly uniform corrosion. In fact, the accelerated corrosion results in Section 5.2 show that all the corrosion damage presented itself in the form of pitting corrosion and that the specimens with the shorter damage length experienced a higher degree of corrosion than the specimens with a longer damage length. Notwithstanding the above differences in experimental approach, all three studies showed that corrosion damaged, patch repaired and FRP strengthened specimens achieved higher static failure loads than the uncorroded specimens. Apart from the different effect that corrosion damage length had in the 3 different studies, the failure modes were also slightly different. The specimens tested by Dladla (2014) and Mundeli (2014) were shown to have failed in a sequence characterized by excessive flexural cracking, debonding of CFRP laminate, followed by crushing of compression concrete and yielding of tension steel. The specimens tested understatic loading in this experiment also experienced excessive flexural cracking, but crushing of compression concrete was encountered prior to CFRP laminate debonding.
However, circular and rectangular openings have been commonly used in practice . When size of opening is concerned, many researchers use the terms small and large opening without any definition or clear-cut demarcation line. Openings of circular, square or nearly square in shape have been defined as small openings . Circular opening may be considered as large when its diameter exceeds 0.25 times the depth of beam web . Classification of opening is based on the structural response of beam. When opening is small enough to maintain the beam type behaviour or in other words the usual beam theory applies. In opposite to this, large opening are those prevent beam type behaviour to develop .
Concrete is the most widely used construction material due to its impressive resistance to compressive load. The major weaknesses of concrete are its brittleness and poor resistance to tensile forces. Intensive number of studies has been conducted to add various types of short discrete fibres into concrete mix to enhance its ductility and post-peak load-bearing capacity. A spiral-shaped steel fibre was recently proposed for reinforcing concrete material with 3D bond components. A series of laboratory tests have been conducted for a comprehensive investigation of the performances of spiral-shaped steel fibre reinforcedconcrete materials and structures. A fundamental understanding of the bond-slip behaviour of spiral fibres and its mechanism of reinforcing the matrix was achieved by conducting pull-out tests. Compressive and direct tensile tests on Ø100-200 mm concrete specimens with spiral fibres of different geometries were conducted for properly determining fibre geometries to reinforce concrete materials. Split Hopkinson pressure bar (SHPB) tests were carried out to study the dynamic behaviour of spiral steel fibre reinforcedconcrete (SFRC) with various volume fractions under compression and splitting tension. The corresponding relations of dynamic increase factor (DIF) vs. strain rate were proposed based on test data. Repeated drop-weight impact tests on SFRC beamsreinforced with the commonly-used hook-end fibres and spiral fibres were performed. Test results demonstrated the superiority of spiral fibres in bonding and enhancing concrete structural elements in resisting impact loads. The even distributions of spiral fibres in comparison with crimped fibres in concrete matrix were justified by physical examinations. Mesoscale simulations with distinctive consideration of mortar matrix, coarse aggregates and spiral fibres were conducted for statistical derivation of dynamic properties of spiral SFRC. While having demonstrated the promising performances of concretereinforced with spiral fibres, further studies are also suggested based on the observations and results obtained.
Generally all the structural members will experience torsion, when the external loads acts away from the plane of bending along with shear and bending moment . Due to this torsion, the shear stresses will occur resulting in diagonal cracks. The design of structural elements should also consider the effect of torsion to counteract the twisting effects. The structures with L shape, T shape, double T shape and box sections are generally experience torsion force. The members which are curved in plan, eccentrically loaded beams and spiral staircase are also have torsion force. Early studies were mostly concentrate only on flexure, shear and bending moments since they believe that the members fails due tension and shear force but actually it accompanied by tension force also. Now the scope of research is becoming wider and now in addition the studies are focusing on the behaviour of members due to pure torsion  is encouraged. This is because the torsion force can cause severe damage than other forces. The design of reinforcedconcretebeams should be provide sufficient reinforcement to accommodate the effects due to torsion. If there is no adequate reinforcement for torsion force, the member will subjected to sudden brittle failure. The main aim of this study is to determine the behaviour of reinforcedconcrete beam with different percentage of longitudinal and transverse reinforcements under torsion force.
Many diagonal cracks can be developed above and below openings in reinforcedconcrete deep beams due to high stress concentration at corners and the abrupt change of the main load path. These diagonal cracks would accelerate the decreasing rate of the effective strength of concrete because of high transverse tensile strains at the diagonal crack plane as pointed out by Vecchio and Collins 11 . Kong et al. 3 and Tan et al. 5 showed that inclined reinforcement around openings is more effective in improving the ultimate shear strength of deep beams with openings than horizontal or vertical reinforcement. To understand the influence of inclined reinforcement on the structural behavior of deep beams with openings, it is necessary to examine the relation between the amount of inclined reinforcement and geometrical condition of beams such as opening size, opening position, and shear span-to-overall depth ratio. However, experimental data available on the amount of inclined reinforcement required to complement the strength reduced by openings are scarce. In this paper, fifteen reinforcedconcrete deep beams with web openings subjected to two point top concentrated loads were tested to failure. The main variables considered were the width and depth of openings, and amount of inclined reinforcement around openings. Four sizes of web openings and three amounts of inclined reinforcement were investigated. To understand the effect of the amount of inclined reinforcement and opening size on the structural behavior of such beams, an effective inclined reinforcement factor was proposed. Also a numerical technique based on the upper bound analysis of the plasticity theory was proposed to estimate the shear strength and load transfer capacity of reinforcement in deep beams with openings
was to enhance understanding of the effect of steel fibres on structural behaviour of RC elements under low and high rates of loading. The material constitutive model proposed by Lok and Xiao (1999) was adopted in order to define the post-cracking tensile stress-strain relationship for SFRC. The load-deflection results understatic loading are presented alongside the ones for RC beams (i.e. without fibres) in Fig. 18. The curves were obtained using a displacement-based loading method with incremental displacements applied at the mid-span of the beam. As it is shown, by adding 1% steel fibres to the concrete matrix, both the load-carrying capacity and stiffness were enhanced. The results were extended to include all loading rates considered and the ensuing load-deflection curves for different loading rates are depicted in Fig. 19. The load-deflection curves clearly demonstrate the enhancement in load-carrying capacity and ductility due to the addition of fibres. A comparison between the values of the peak loads and deflections (for RC beams and their counterpart SFRC ones) is summarised in Table 3. The results show that the addition of fibres leads to an increase of both strength and ductility (with the maximum load and deflections used to denote these two key structural performance characterises, which have particular importance for impact-resistant design). The enhancement changes depending on the loading rate applied, ranging from 40% to 74% when the load is applied monotonically (similar trends were found when the load applied as a pulse, i.e. when the actual failure point was sought under impact loading as explained earlier). The enhancement to ductility is as high as 4.8 times the one associated with RC for monotonic loading (and 5.7 for pulse loading). The lowest value for ductility increase due to fibres was found to be ~2.9, which is still a significant improvement. A comparison
Recently, an experimental test was conducted to investigate the cracking behaviour of beams strengthened by CFRP and TRC (Hauhuar et al., 2017). It showed that concretebeams strengthened using TRC experienced similar cracking behaviour to the beams strengthened by CFRP. TRC can also improve load carrying capacity of beam up to 27% (Truog et al., 2017). However, limited findings related to TRC strengthened beams with openings have been reported. In this study, an experimental test was conducted on unstrengthened and strengthened concretebeams with openings. The aim of this study is to investigate the flexural behaviour of strengthened concretebeams with circular and square openings. Analyses on beam strength, deflection, crack patterns and failure mode of the beams were discussed.
The experimental test set-up of GFRP RC beamsunderstatic loading involved placing the beams between two steel I-beams with a clear span of 2 m. There was a 200 mm overhang at each side. The beams were set up to have simply supported conditions, with a pin support at one end and a roller support at the other end. The simply supported condition allowed the GFRP RC beams to deflect under loading as shown in Fig. 5 and Fig. 6. The GFRP RC beams were displacement controlled, loaded at a rate of 1 mm/min. The loads were applied at 667 mm from each support, using a steel spherical ball placed at the centre of the steel I- beam. The 1000 kN hydraulic controlled load cell used during testing had a smaller load cell attached to the underside. The smaller load cell captured smaller load increments applied to the GFRP RC beams. Mid-span deflection was measured by a linear potentiometer attached to the under-side of each GFRP RC beam. The test data were recorded using the high speed data acquisition system, NI PXIe-1078.
The present paper reports test results of nine two-span RC deep beams . The tested variables were shear span-to-depth ratio, vertical web reinforcement ratio, horizontal web reinforcement ratio, and concrete compressive strength. The specimens were tested in a compression machine where increasing monotonic staticloads were at each mid-span. All tested beams were loaded until failure. The failure planes evolved along the diagonal crack formed at the concrete strut along the edges of the load and intermediate support plates. The test results were measured at different loading levels for the mid-span deflection, mid- span bottom steel strain, middle-support top steel strain, middle-support stirrups strain, and end-support stirrups strain. Also, the cracking patterns were identified. The effects of testing variables on the first diagonal crack load, ultimate shear load, deflection, stiffness, and failure mechanisms were studied. Finally, the obtained test results are compared to the predictions of finite element analysis for continuous deep beams and a well agreement between the experimental and analytical results was found.
Natural hybrid fiber reinforcedconcrete (NHRFC) is most economical alternative by reducing both the total volume of concrete and the amount of steel required for a structural member. Addition of fibers in concrete improve the tensile characteristics by inhibiting crack growth and increase in toughness or energy absorption capacity, flexural strength, fatigue resistance and ductility. Various types of fibers were used in concrete such as metallic fibers, polymeric fibers, mineral fibers, and naturally occurring fibers, among these natural fibers (coir and human hair) are giving better due to their easy availability and tensile strength. It has been shown recently that many researchers investigated the mechanical properties of the concept of hybridization with two different fibers incorporated in a common cement matrix, and the hybrid composite can offer more attractive engineering properties, because the presence of one fiber enables the more efficient utilization of the potential properties of the other fiber. Addition of Nano material (Nano silica) to the concrete matrix to increase the compressive strength of the concrete and reduce the porosity between the cement particles. Nano Silica is used for improving the concrete properties in fresh and hardened states. The use of two or more different types of fibers in concrete matrix is called hybrid fiber reinforcedconcrete. Hybrid fiber reinforcedconcrete (HFRC) is the one in which more than one or two types of fibers are used as secondary reinforcement. In this project coir and human hair are used as hybrid fiber reinforcement to the concrete slab specimen.
Firstly, observations made by means of visual inspection suggest that none of the BFRP rebar reinforcedconcretebeams were affected by the rebar slippage phenomenon, as BFRP rebar experienced elongation and spiral de-bonding only at the point of shear failure . Furthermore, emphasis must be put on the distinct difference in failure modes between beamsreinforced with BFRP rebar and traditional steel rebar. Although the reinforcement setting-out was virtually identical for both, steel and BFRP rebar reinforcedconcretebeams, the control beam B1 failed in compression and all other BFRP reinforcedconcretebeams failed in shear. This was dictated by the BFRP rebar higher tensile strength. Analysis undertaken in appendix Error! Reference source not found. and Error! Reference source not found. show that the neutral axis position of the beam B1 was calculated to be 15mm from the top of the section. The neutral axis of the BFRP reinforcedbeams was calculated to be 30mm from the top of the section. It was established earlier that with the advancement of the cracking, the neutral axis moves upward towards the top of the section (refer to 6.4.1). The lower position of the neutral axis of the BFRP reinforcedconcrete beam allowed for greater compression resistance under the same strength class concrete. Thus, the shear failure occurred before beam failed in compression.
Epoxy resin are generally low molecular weight pre-polymers capable of being processed under a variety of conditions. Two important advantage of these resin over unsaturated polyester are: First they can be partially cures and stored in the state and they exhibit low shrinkage during cure. It is a 100% solids low viscosity epoxy resin able to cure in the presence of moisture and at temperatures as Low as 2 ̊C. The chemical resin has high chemical and corrosion resistance, good mechanical and thermal properties. It has two components, A – resin and B – hardener. Ratio of the components by weight is 100 parts of component B to 50 parts of component A shown in fig 1. Mixing is done thoroughly for 5 min with low speed mixer at 400 rpm until components are thoroughly dispersed. The properties of epoxy are mention in Table 2.
The measured amount of load transferred to the end support is listed in Table (2) for all tested beams. From external equilibrium of forces and symmetry, the measured reaction at intermediate support is evaluated in the table. Linear elastic analysis was performed using SAP program for beams in order to assess the reactions of supports. From elastic analysis, the reactions of the exterior and intermediate supports due to the total applied load (P) are 0.175P and 0.65P respectively. It was stated before (Ashour et al. 2000) that the differential settlement had no significant effect on the elastic behavior of continuous deep beams, and would have less significance at higher loads in any case. Fig. 10 shows the measured amount of the load transferred to the end and intermediate supports against the total applied load for beams having constant (a/d) value of 1.0 and different web reinforcement ratios. On the same figure, the reactions at support are obtained from elastic analysis are also presented. Although the amount of web steel influences the maximum reaction at support, it has no effect on the total load-support reaction gradient. Before the first diagonal crack, the relationship of the end and intermediate support reactions against the total applied load in all tested beams shows good agreement with elastic prediction. The amount of loads transferred to the end support, however, was slightly higher than that predicted by the elastic analysis after the occurrence of the first diagonal crack within the interior shear span. At failure, the difference between the measured end support reaction and prediction of the elastic analysis was in order of 8%, 10%, and 14%, for beams with (a/d) of 0.77, 1.0, and 1.25, respectively.
The nonlinear finite element program; ANSYS 10 was used to predict the behavior of tested deep beams. A correlative study based on the load- deflection response as well as the cracking patterns was conducted to verify the analytical model with the obtained experimental results. In the finite element discretization of the tested beams, a 50x50 mm mesh of eight-node brick elements (Element 65) was used for concrete. The top & bottom flexural steel bars and the horizontal & vertical web reinforcement were represented by bar elements. The area and spacing of such bar elements were similar to the experimental specimens. The concentrated loads were also applied to the top surface at mid-span of the tested beams. The supports were represented by restrained nodes at the corresponding locations. To model concrete behavior, nonlinear stress- strain curves were used in compression and tension. Such models account for compression & tension softening, tension stiffening and shear transfer mechanisms in cracked concrete. An elasto-plastic model was used for steel in compression and tension. The initial Young’s modulus in concrete was taken as 22 GPa; and the steel modulus was 200 GPa. An incremental-iterative technique was employed to solve the nonlinear equilibrium equations. The load increment was set at 5% of the experimental ultimate load. The load increment was subject to adjustment to obtain results at certain specific load levels. The maximum number of iterations was set to 20 in each load step and the equilibrium tolerance of 0.5% was chosen.
During the analysis, all beams showed flexural crack initiated from the mid-span on the underneath surface of the beam. The crack signs appear as vertical lines. The crack mouth widens and penetrated into the beam, towards the compressive zones. The diagonal tensile cracks occurred at between support and mid span which occur mostly in the longitudinal direction. When the principal stresses exceed the ultimate tensile strength of the concrete, compressive cracks appear perpendicular to the principal stresses. It is seen that crack width and crack lengths between SFRC beam and SFRC (TZ) beam are similar. Although SFRC (TZ) beam can resist less maximum applied load compared to SFRC beam, the steel fibre placed at the tension zone only, can function similarly to SFRC beam. Steel fibre holds the concrete matrix well and reduces the flexural cracks propagation. All beams failed under flexure.