Improving the Properties of Self-compacted Concrete with Using Combined Silica Fume and Metakaolin

The viscosity is the main property of self- compacted concrete (SCC) and using of pozzolan material such as metakaolin (MK) and Silica fume (SF) can help to achieve that goal. The effect of simultaneous substitution of MK and SF instead of cement on the rheological and mechanical properties of self-compacted concrete was experimentally investigated in this paper. Seventeen mix designs were cast with a substitution weight percentage (5, 10, 15, 20 %) in water to adhesive material ratio equal 0.32. All mixes were examined by compressive, tensile strengths and water absorption tests with an appropriate fluidity, without having signs of segregation or instability. The test results were indicated that the SCC mixes containing MK and SF had higher compressive and tensile strengths in comparison with no-pozzolan concrete. The comparison of linear multiple regression techniques (LMRT) and nonlinear multiple regression technique outputs with experimental results showed an appropriate similarity

Finding Critical Element in the Progressive Collapse of RC Structures Using Sensitivity Analysis

Failure of some elements in the structure can play triggering role for beginning of collapse progression. The critical element is the structural element that when it fails, leads to progressive collapse. To find the critical element of the structure, sensitivity analysis should be done. But there are not specific structural criteria for using in sensitivity analysis. In this paper following GSA, UFC 4-023-03 and ASCE guidelines, sensitivity analysis has been modified and applied to find the critical element of a major number of reinforced concrete structures. 1080 3D nonlinear pushdown analyses were done and the results showed that the place of the critical elements differs in different stories and different plan shapes of high rise structures. In the structures with high aspect ratio in height, the critical element of the whole structure is located in the story of 2/3 height of the structure. When the aspect ratio of the structure in plan increases, sensitivity of the columns in the long dimension of the structure become closer to each other

INVESTIGATION OF DESIGN CODES RELIABILITY FOR SEISMIC DESIGN OF STEEL PLATE SHEAR WALLS CONSISTING OF SEVERAL PARAMETERS

Steel plate shear walls have been used as lateral resistant systems at several buildings particularly at high rise building during past three decades. This system contains appropriate rigidity to control displacements and also have ductile failure and high energy dissipation mechanism, so it can be used for new buildings or strengthening existing structures at seismic prone areas. Generally steel plate shear walls are consisting of steel plate walls and two boundary columns and horizontal floor beams. In this paper, initially a steel plate shear wall of a 5-floor building at high seismic area was designed according to AISC 341-05, then ABAQUS finite element program was used to investigate the seismic behavior of structure and get hysteresis curves under cyclic loading and also investigate the several parameter effects on local instability and non-linearity of material at designed typical shear wall and also the other new walls with different opens and rigidities. Numerical analysis results indicate that rigidity, shear capacity, and energy dissipation of wall were increased whenever column dimensions and length to height ratio was increased. Moreover, the main failure mode as global buckling was happened at the base of the column with increasing of the number of floors, so indicating the decreasing capacity and rigidity. And also the results showed that more open dimensions caused the higher ductility, decreasing capacity and rigidity and dissipation. The higher capacity, rigidity, energy dissipation, and ductility were observed at shear wall consisting of the more stiff nesses

Damage Detection of Reinforced Concrete Shear Walls Using Mathematical Transformations

Structural health monitoring is a procedure to provide accurate and immediate information on the condition and efficiency of structures. There is variety of damage factors and the unpredictability of future damage, is a necessity for the use of structural health monitoring. Structural health monitoring and damage detection in early stages is one of the most interesting topics that had been paid attention because the majority of damages can be repaired and reformed by initial evaluation ,thus the spread of damage to the structures, building collapse and rising of costs can be avoided .Detection of concrete shear wall damages are designed to withstand the lateral load on the structure is critical .Because failures and  malfunctions of shear walls can lead to serious damage or even progressive dilapidation of concrete structures .Change in stiffness and frequency can clearly show the damage occurrence. Mathematical transformation is also a tool to detect damage. In this article, with non- linear time history analysis, the finite element model of structures with concrete shear walls subject to four earthquakes have extracted and using Fourier and wavelet transform, the presence of shear walls is detected at the time of damage

Evaluation of new composite rigid joint under cyclic loading and its effect on one-floor composite frame

In order to improve the performance of structure against lateral and gravity loads, new systems known as composite systems consisting of the reinforced concrete columns and steel beams (RCS) can be used and thereby the advantages of concrete beside steel are acquired. RCS joints can be implemented as either through-beam-type joint or through-column-type joint. In this paper, a concrete joint as standard reference joint and a proposed composite joint through-column‎ with new details were built and tested under cyclic loading. Then, using numerical analysis by finite element method, the behavior of composite joint under cyclic loading has been studied and the behavior and performance of proposed composite joint has been studied by comparing the results with that of concrete joint. The results showed that the joint composition in this way resulted in decreasing of the compressive and tensile damages of concrete and increasing in loading capacity, ductility, stiffness and energy absorption. General results of application of composite joint at the one floor-one span composite frame indicating that lateral loading capacity of frame was increased and the performance of frame was improved

Study on the Nonlinear Behavior of Strengthened RC Frames using Steel Prop and Crub in Connections and Strengthening of Beam and Column

One of useful methods for strengthening for reinforced concrete frames, is to use steel prop and crub in connections, alone or combined with beam's revival steel sheets and column jacketing with steel sheets or profiles. In this paper, after modeling and verifying application of model, behavior of RC frames, strengthened with this method was studied. For this purpose, a RC frame has been strengthened in 4 general ways (crub and prop, crub and prop with revival sheet among two beamâs crub, crub with column jacketing in the bottom of columnâs crub region, combination of three mentioned moods) with three different propâs sectional area. Results showed that using crub and prop increases stiffness and strength of frame, significantly. If crub and prop are used with column jacketing for strengthening RC frames, framesâ strength increase up to 3.3 times of ordinary frame. Adding beam revival sheet to crub and prop, causes sooner yielding and bulking in compressive prop

Flexural Capacity Prediction of RC Beams Strengthened in Terms of NSM System Using Soft Computing

In recent years, there has been a notable increase in the application of near-surface mounted fiber-reinforced polymer (FRP) reinforcement in reinforced concrete structures. Nevertheless, there is a discernible disparity in the accessibility of accurate and customize measures for augmenting flexural strength through the use of near-surface mounted (NSM) reinforcement techniques. Although several basic models have been proposed to predict the flexural capacity achievable with this technology, established codes have not yet provided mathematical equations for this specific purpose. This study presents two separate methodologies with the objective of enhancing the development of suitable code provisions. In the first stage, A comprehensive and reliable database has been developed to leverage the predictive accuracy of neural networks in the computation of the flexural capacity of reinforced beams that utilize near-surface mounted reinforcement. Following this, the results obtained from the neural network are employed to construct a linear equation using the group method of data handling (GMDH) technique. The presented equation has been carefully formulated to produce a concise and simple mathematical expression that enables the determination of the flexural strength of a beam on the field. The evaluation of the accuracy and effectiveness of both the neural network and the suggested equation is conducted in accordance with the requirements specified in ACI 440.R2 for externally bonded reinforcements. The neural network's prediction has a mean absolute error of just 5% in comparison to the experimental results and the GMDH equations exhibit a noteworthy level of concurrence with the experimental outcomes, as they display a mean absolute error of 16%

Innovative Hybrid Reinforcement Constituting Conventional Longitudinal Steel and FRP Stirrups for Improved Seismic Strength and Ductility of RC Structures

The use of fiber reinforced polymer (FRP) reinforcement is becoming increasingly attractive in construction of new structures. However, the inherent linear elastic behavior of FRP materials up to rupture is considered as a major drawback under seismic attacks when significant material inelasticity is required to dissipate the input energy through hysteretic cycles. Besides, cost considerations, including FRP material and construction of pre-fabricated FRP configurations, especially for stirrups, and probable damage to epoxy coated fibers when transported to the field are noticeable issues. The current research has proposed a novel economical hybrid reinforcement scheme for the next generation of infrastructures implementing on-site fabricated FRP stirrups comprised of FRP sheets. The hybrid reinforcement consists of conventional longitudinal steel reinforcement and FRP stirrups. The key feature of the proposed hybrid reinforcement is the enhanced strength and ductility owing to the considerable confining pressure provided by the FRP stirrups to the longitudinal steel reinforcement and core concrete. Reinforced concrete beam specimens and beamcolumn joint specimens were tested implementing the proposed hybrid reinforcement. The proposed hybrid reinforcement, when compared with conventional steel stirrups, is found to have higher strength, stiffness, and energy dissipation. Design methods, structural behavior, and applicability of the proposed hybrid reinforcement are discussed in detail in this paper