نشریه مصالح و سازه های بتنی
سال سوم شماره 2 (پیاپی 6، پاییز و زمستان 1397)

Performance of reinforced concrete frames is highly depended on detailing of the ductile connections based on the philosophy of strong column-weak beam. There are several methods for seismic upgrading of connections. In this paper, using steel jacketing for seismic upgrading of Concrete Beam-Column connections subjected to constant axial and cyclic loads has been investigated using finite element method. Some experimental results are used to verify the finite element approach. Analyses are then conducted on main models upgraded with steel jackets in beam, column or both using parameters like beam jacket thickness, column jacket thickness and axial load ratio. The results are compared and the suitable model is proposed. Based on different analysis for the considered samples, several results obtained. Analysis result shows the positive impact of the use of steel jacketing for upgrading of Concrete Beam-Column connections. From these results, it can be noted that, regardless of the size of the axial load, using a steel plate increased the tangential rigidity of connection. And this increasing of rigidity in most cases is more than of increasing of final capacity of the connection. But in the case of high axial loads, the increase that can be seen in the final capacity of the connection is further of rigidity increasing. Also, depending on the size of the axial load, steel plate can increase the capacity of connection up to 7 time, and the capacity and ductility of connections was returned to better state with the average axial load.

Abstract One of the important issues concerning the cement mixtures is the durability against several destructive factors such as chloride induced corrosion and sulfate attack, which can in some way result in concrete deterioration. In the current experimental study, the effects of polyethylene vinyl acetate and polyvinyl acetate on the durability of clacium aluminum cement based mixtures have been investigated and evaluated. In this study, the test results including compressive strength, permeable pores, rapid chloride migration coefficient and the compressive strength of sulfuric acid-treated mixtures have been reported. The results suggest that the polymers of ethylene vinyl acetate and polyvinylacetate can reduce the penetration rate of water and chloride ion migration in cement based mixtures and ethylene vinyl acetate outperformed the polyvinyl acetate in enhancing these properties. The polymers reduced compresssive strength noticeably at early ages, however at later ages the differences between the compressive strengths of the polymer modified and plain mixure were reduced, even at high percentages of incorporation (25%).

Sequential quakes as shock-aftershocks result in nonlinear response of buildings and in many cases lead to severe destruction such as accumulative structural damages in compare to single shock quakes. In current study, the shock-aftershock sequence effect on the nonlinear seismic performance of reinforced concrete (RC) moment frames is studied in detail. In this way, nonlinear numerical method is selected as the study approach and preliminary models are calibrated based on existing shake-table experiments. In advance, four-story and eight-story frames are modeled using flexibility-based finite element code and are subjected to quake sequences. Three types of seismic sequences are assumed for study: (1) single shock quakes; (2) similar shock-aftershock quakes; (3) dissimilar far field-near fault shock-aftershock quakes. Discussions are based on the maximum and residual inter-story drift ratios. Results reveal that the residual drifts are increased in seismic sequences. In addition, four-story frames experience higher maximum drift ratio than the eight-story frames during the aftershocks. The increase of residual drift ratio in more apparent for four-story frames than eight-story frames in the case of dissimilar seismic sequences. For all the assumed cases, top stories experience the highest values of maximum and residual drift ratios which show the sensitivity of top stories to the seismic sequence. Thus, the collapse probability of top stories is high during shock-aftershock sequences and needs to be considered in further seismic design.

The chloride ingress into concrete and corrosion of steel reinforcement due to wetting/drying (WD) cycles is a main issue caused to decline the service life of reinforced concrete structures. In this paper, the effects of WD cycles on chloride penetration in concrete were studied using a finite element based numerical model. The results showed that the chloride ingress into concrete increased with increasing in daily WD cycles. The chloride concentration after 10 years at depth of 50 mm and the maximum chloride concentration of the submerged specimen were 2.4 and 2.0 times lower than the specimen exposed to 2 and 24 WD cycles, respectively. These ratios increased up to 4.2 and 3.7 when the WD cycle increased to 24 cycles. The numerical model outputs also indicated that the chloride concentration at depth of 50 mm and the maximum chloride closely tended up to a constant amount by increasing the number of WD cycle up to 100 cycles (similar to splash condition).

The rehabilitation of existing reinforced concrete structures and infrastructures becomes necessary due to ageing, corrosion of steel reinforcement, defects in construction/design, demand in the increased service loads, and damage in case of seismic events and improvement in the design guidelines. Fiber-reinforced polymers (FRP) have emerged as promising material for rehabilitation of existing reinforced concrete structures. The use of externally bonded Fiber Reinforced Polymer (FRP) sheets is an effective technique for strengthening and retrofitting of reinforced concrete beams especially under flexural loads. The use of FRP has been on the rise, mainly due to composite materials’ high strength and stiffness, non-corrosive nature and ease of installation. The purpose of retrofitting is to structurally treat the member with an aim to restore the structure to its original strength. Few investigations have performed to investigate the characteristics of retrofitted reinforced concrete flexural members. In the present study, a method for analyzing of the reinforced concrete beams retrofitted by FRP is proposed. The equilibrium equations and associated strain boundary conditions are used to determine the deflection and moment at each point along beam. As it is demonstrate in the numerical example, the proposed procedure can yield in efficient way, accurate result for FRP concrete beams.

Considering the mandatory application of lightweight concrete AAC blocks in separating walls of buildings, the need for proper selection and installation of such materials for suitable operation and prevention of material losses and additional costs related to future restoration should be considered. In this study, first, the compressive strength of blocks was determined by testing of cubic samples with dimensions of 200 mm. The results show that minimum and maximum compressive strengths was 2.4 and 3.1 with an average value of 2.7 MPa. To determine the modulus of elasticity of the blocks, cubes of 100 mm dimensions were also tested under compressive loading while both applied load and corresponding deformation were acquired. The process of determining cement-based block adhesive strength was done by testing 28 block prisms with dimensions of 100 x 100 x 200 mm, which were glued together with adhesive, under three-point bending set up at specified times from 8 hours to 35 days. The results were compared with control samples with dimensions of 100 × 100 × 400 mm. The results showed that, after 48 hours, adhesive adhesion strength exceeded the resistance of the block.

Due to the influences of several parameters such as brick and mortar properties, interaction between brick and mortar and etc., engineers encounter challenges in modeling and evaluating procedure of the seismic behavior of masonry-infilled reinforced concrete (RC) frames. To predict the seismic behavior of these structural elements, the analytical model must be comprehensive and efficient in such a way that it can show the actual behavior of the structure. Modeling the behavior of masonry infilled reinforced concrete frames under in-plan load, has received much attention over the last decade. The main aim of this paper compares different methods of modeling infilled frame with experimental results in order to choose the appropriate method for modelling of infilled RC frames. To achieve the purpose, after describing the background to the application of each method, the specimen which was tested in the laboratory was modeled in three different methods. The first model was realized by simplified micro-modelling and, the second model was realized by macro-modelling procedure via Abaqus software. The third model was further made by equivalent diagonal compressive strut modelling in OpenSees software. The results showed that the macro-modeling method had maximum and the simplified micro-modeling had minimum accuracy in Abaqus software. The amount of observed differences between experimental results and macro-modeling approach, between experimental results and simplified micro-modeling approach, and equivalent diagonal compressive strut modeling were 2.65%, 9.25% and 10.12%, respectively. These findings maintain that macro-modeling technique in Abaqus software could have an appropriate performance in detecting cracks.

Production of cement as the main components of concrete is an energy consumption process with environmental pollutions. Application of cementitious materials is one of the major solutions for mitigation of subside the environmental problems and economics of concrete production leading to more durable concrete structures. This paper tries to assess the application of pozzolanic materials, namely micro silica and natural zeolite for this means. A two-phase experimental study conducted which at the first stage, an optimization process utilized to verify the proper blended binder system in binary and ternary terms. At the second phase the mechanical and durability aspects of the blended system experimentally investigated which propose the enhancements on the durability of concrete mixtures.