With the ongoing developments in numerical analysis methods, it is possible to model the soil-foundation-structure interaction and non-linear load-deformation behavior of soils in three-dimensional calculations. In light of these developments, the calculations of mat foundations can be made more realistically and economically by using advanced softwares, which take into account the interactions of these three components than the conventional methods. The aim of this paper is to present the effect of superstructure loading types on the analysis of mat foundations by using three dimensional finite element analysis results. Thirty six different models have been established to examine these effects on the internal forces and settlement behavior. The data of a 3-storey existing building has been used and superstructure loads have been modeled in different ways such as uniformly distributed loads, column loads and by modeling all building. The building has been modeled with a mat foundation having a thickness of 50 cm, 75 cm and 100 cm in seperate models. The mat and superstructure elements have been modeled either with 2D plate elements or 3D volume elements in different models. The “Mohr-Coulomb” material model has been used and soil properties have been represented as “normally loaded” and “overconsolidated”. Results for total and differential settlements and internal forces have been presented in figures and graphs. An important finding is the place where the maximum displacement occurs. It is very different when the load is transmitted by modeling the whole structure and it causes to have different internal forces and different placement of reinforcement. Another finding is that the biggest decreases in differential settlements are seen in column and building loading when the soil properties improved, while this effect remains very small in distributed loading. For bending moments, the biggest difference in comparison to the loading types is that the maximum moments are calculated in different places independent to the location of shear walls, when the load is simulated as a uniformly distributed load. It has been found that the superstructure loading type affects the settlement pattern and internal forces, so this effect must be taken into account.

A fast converging and fairly accurate nonlinear simulation method to assess the behavior of reinforced concrete columns subjected to static oriented pushover force and axial loading (sections under biaxial bending moment and axial loading) is proposed. In the proposed method, the sections of column are discretized into “Variable Oblique Finite Elements” (VOFE). By applying the proposed oblique discretization method, the time of calculation is significantly decreased and since VOFE are always parallel to neutral axis, a uniform stress distribution along each oblique element is established. Consequently, the variations of stress distribution across an element are quite small which increases the accuracy of the calculations. In the discretization of section, the number of VOFE is significantly smaller than the number of “Fixed Rectangular Finite Elements” (FRFE). The advantages of using VOFE compared to FRFE are faster convergence and more accurate results. The nonlinear local degradation of materials and the pseudo-plastic hinge produced in the critical sections of the column are also considered in the proposed simulation method. A computer program is developed to calculate the local and global behavior of reinforced concrete columns under static oriented pushover and cyclic loading. The proposed simulation method is validated by the results of tests carried out on the full-scale reinforced concrete columns. The application of the “Components Effects Combination Method” (CECM) is compared with the proposed “Simultaneous Direct Method” (SDM). The obtained results show the necessity of applying SDM for nonlinear calculations. Especially during the post-elastic phase, which occurs frequently during earthquake loading.

Efflorescence formation is an important soundness issue to be considered with alkali-activated cements. In this study, the impact of activator type on the efflorescence formation severity and methods of efflorescence reduction in alkali-activated phosphorus slag cement are investigated. Different alkaline activators including NaOH, KOH and liquid sodium silicate of different silica modules (Ms = SiO2/Na2O) were used for alkali-activation of phosphorus slag. Additions of high alumina cements (Secar 71 and 80) and application of hydrothermal curing condition at 85 °C for 7 h with different pre-curing times (1, 3 and 7 day) in humid environment (relative humidity of 95 %) and 25 °C were used for efflorescence control in alkali-activated phosphorus slag cement. Sodium containing activators resulted in more severe efflorescence formation compared with those of potassium containing activators. Also presence of liquid sodium silicate intensified efflorescence formation. Based on the results obtained, application of an optimum pre-curing stage in humid environment before hydrothermal curing regime stabilizes the cement matrix and improves the effectiveness of hydrothermal conditions.

Replacement of existing unreinforced masonry (URM) walls, commonly used as a non-structural member in apartments, with new reinforced concrete (RC) components has been used as a reliable method when remodeling is carried out. However, special care needs to be taken when URM walls are removed not to waste construction time and materials. Therefore, retrofitting existing URM walls can be deemed a better solution rather than replacing URM walls with RC ones. Using shotcrete is one of retrofitting techniques of URM walls. However, using normal shotcrete cannot improve adequate ductility and may cause brittle failure at a wall-frame or slab connection. Therefore, new materials such as engineered cementitious composite (ECC) and ultra-high performance concrete (UHPC) have emerged to resolve the problem of normal shotcrete by increasing ductility and toughness of retrofitting materials. In this study, sprayed ECC was used to increase both strength and ductility of existing URM walls. The results of two retrofitted URM walls under lateral quasi-static loading were compared to non-retrofitted one. One strengthened wall, retrofitted masonry wall (RTM)-ECC, was just sprayed and anchored to a wall base. Another strengthened wall, RTM-ECC-WM, was the same as RTM-ECC except for addition of wire mesh. The retrofitted specimens showed significant increase of strength, ductility, and energy dissipation capacity in comparison with the control one. In addition, RTM-ECC-WM indicated better strength degradation due to the load transferring effect of wire mesh than RTM-ECC.

Complex nature of diagonal tension accompanied by formation of new cracks as well as closing and propagating preexisting cracks has deterred researchers to achieve an analytical and mathematical procedure for accurate predicting shear behavior of reinforced concrete, and there is the lack of a unique theory accepted universally. Shear behavior of reinforced concrete is studied in this paper based on recently developed constitutive laws for normal strength concrete and mild steel bars using nonlinear finite element method. The salient feature of these stress-strain relations is to account the interactive effects of concrete and embedded bars on each other in a smeared rotating crack approach. Implementing the considered constitutive laws into an efficient secant-stiffness based finite element algorithm, a procedure for nonlinear analysis of reinforced concrete is achieved. The resulted procedure is capable of predicting load-deformation behavior, cracking pattern, and failure mode of reinforced concrete. Corroboration with data from shear-critical beam test specimens with a wide range of properties showed the model to predict responses with a good accuracy. The results were also compared with those from the well-known theory of modified compression field and its extension called disturbed stress field model which revealed the present study to provide more accurate predictions. 

In this paper, self-consolidating concrete (SCC) mixtures are considered for airfield concrete pavements. A series of rheological, mechanical, transport and frost action durability tests were conducted on the prepared SCC mixtures with and without chemical air entraining agents (AEA). Mineral admixtures including slag, fly ash, silica fume and metakaolin were included in SCC mixtures. The results showed that application of mineral admixture led to significant improvements on the performance of airfield concrete pavement mixtures. Moreover, the performance of mixtures against frost action upgraded when AEA included in companion with the mineral admixtures.

A nonlinear Finite Element (FE) algorithm is proposed to analyze the Reinforced Concrete (RC) columns subjected to Cyclic Biaxial Bending Moment and Axial Loading (CBBMAL). In the proposed algorithm, the following parameters are considered: uniaxial behavior of concrete and steel elements, the pseudo-plastic hinge produced in the critical sections, and global behavior of the columns. In the proposed numerical simulation, the column is discretized into two Macro-Elements (ME) located between the pseudo-plastic hinges at critical sections and the inflection point. The critical sections are discretized into Fixed Rectangular Finite Elements (FRFE). The basic equilibrium is justified over a critical hypothetical cross-section assuming the Kinematics Navier’s hypothesis with an average curvature. The method used qualifies as a “Strain Plane Control Process” that requires the resolution of a quasi-static simultaneous equations system using a triple iteration process over the strains in each section. In order to reach equilibrium, three main strain parameters (the strains in the extreme compressive point, the strains in the extreme tensile point and the strains in another corner of the section) are used as three main variables. The proposed algorithm has been validated by the results of tests carried out on full-scale RC columns. The application of the Components Effects Combination Method (CECM) is also compared with the proposed Simultaneous Direct Method (SDM). The results obtained show the necessity of applying SDM for the post-elastic phase, which occurs frequently during earthquake loading.

Concrete filled steel tube is constructed using various tube shapes to obtain most efficient properties of concrete core and steel tube. The compressive strength of concrete is considerably increased by the lateral confined steel tube in circular concrete filled steel tube (CCFT). The aim of this study was to present an integrated approach for predicting the steel-confined compressive strength of concrete in CCFT columns under axial loading based on large number of experimental data using artificial neural networks. Neural networks process information in a similar way the human brain does. Neural networks learn by example. The main parameters investigated in this study include the compressive strength of unconfined concrete (f'c), outer diameter (D) and length (L) of column, wall thickness (t) and tensile yield stress (fy) of steel tube. Subsequently, using the reliable network, empirical equations are developed for the confinement effect. The results of proposed model are compared with recently existing model on the basis of the experimental results. The findings demonstrate the precision and applicability of the empirical approach to determine capacity of CCFT columns.

In this study, the effects of high temperatures on the mechanical and microstructural properties of high strength concretes (HSCs) made with metakaolin (MK) are investigated. For this purpose, the concrete mixtures made with MK were produced with water-binder ratio of 0.2. The mechanical properties of these concretes at 25, 250, 500 and 750 oC temperatures were determined. Besides, the effect of high temperature on the microstructural changes of cementitious matrix, interfaces between aggregate particles-cementitious materials and aggregates of these concretes were inspected by X-ray diffraction, scanning electron microscope and plane polarized transmitted light (PPTL) analyses. The results indicate that the ultrasound pulse velocity, compressive strength, flexural strength and splitting tensile strength values of these concretes decrease especially depending on the increase of the high temperature after 250 oC. The heated concrete specimens were also examined at both macro and micro scales to determine the discoloration, alteration and cracks of HSC at different temperatures. PPTL analyses show that increasing temperature cause impairing of interfaces between aggregate particles and cementitious materials. The results also show that the partial replacement of MK with cement has the best performance on the mechanical properties of HSC.

Concrete flat roof defects such as water leakage present a significant and common problem in large building, particularly in tropical countries, where rainfall is high. To monitor this condition, effective non-destructive test methods are required to detect problems at an early stage, especially hidden defect within the concrete roof, which are critical. This paper presents the potential use of electromagnetic (EM) waves for determining possible leakage of the concrete flat roof as a result of failure of the waterproof membrane layer. This study was assessed, experimentally by investigation of the propagation of EM waves through the roof and their interaction with water. Novel Microwave sensors described in the paper operates in the 6 GHz to 12 GHz frequency range using a Marconi 6200A microwave test set. A range of existing current methods were overviewed and analysed. Results of experimental tests confirmed that microwaves could be used as an alternative non-destructive method for identifying water ingress caused by membrane failure into the concrete roof.

The determination of the parameters of concrete (i.e., elasticity modulus, tensile strength) is very crucial task in material engineering. For this purpose, in general, structural codes propose some empirical formulas to estimate the parameters of materials and is useful for designers rather than the experimental process. However, the estimated results usually vary for different standards. Hence, this research paper aims to compare the elasticity modulus formulas considering six standards (TS 500, ACI 318M-05, CSA A23.3-04, SP 52-101-2003, EN 1992-1-1 and AS-3600-2001) with experimental elasticity modulus test results. In the evaluation of the results, the TS 500 and EN-1992-1-1 overestimate the elasticity modulus and the SP-52-101-2003 estimates the values more close to experimental results. In addition, a new equation for modulus of elasticity including the compressive strength and the density is derived for RAC. Also, in this paper energy capacities of concretes (elastic energy capacity, plastic energy capacity and toughness) are evaluated considering compressive strength test data. As a result, according to energy capacities of concretes, the proportions 5% silica fume (SF) and 30% recycled aggregate are proposed as the optimum ratio.

Pre-cast concrete products are sometimes manufactured in 2 cycles per day with one mold for the purpose of productivity improvement and so forth. In such a case, from the point of view of securing early-time strength which is required at the time of demolding, it is necessary to increase steam curing temperature and then the likelihood of temperature cracking becomes a concern. Moreover, self-compacting concrete (hereinafter refer as “SCC”) is increasingly used to which ground granulated blast-furnace slag is added, in consideration of environment surrounding a plant or operation environment. One choice then is to admix expansive agent in order to prevent cracking due to autogenous shrinkage. However, there is some possibility that high temperature curing required for 2 cycles per day production likely enhances cracking due to expansive agent admixing. In this study, the cause of cracking of large-sized pre-cast concrete products with high amount of expansive agent, in comparison of 1 cycle per day and 2 cycles per day productions was investigated.

As the result, it was confirmed that high temperature steam curing and early demolding of 2 cycles per day production promote thermal stress cracking in contrast to 1 cycle per day production, and at the same time, un expected cracking along main reinforcement is caused by excess expansion due to inappropriate curing of expansive agent.

This paper outlines the effects of curing conditions on the strength and hydration products of lime activated slag cement. The slag cement was prepared by activating the ground granulated blast furnace slag with lime and plaster of Paris. The curing of mortar specimens was done at temperatures of 27⁰, 45⁰,60⁰,75⁰C and the compressive strength of specimens were determined after curing periods of 3,7, 28, 56 and 90days. The curing temperature is found to influence both the early and later age strengths. For the present test conditions the highest 90days compressive strength was found to be 47.63MPa for the specimen cured at temperature of 60⁰C. Further, the developed strength in mortar specimens were correlated with the hydration products and microstructure using X-ray diffraction and scanning electron microscope results. Generalized reduced gradient technique is adopted to find the optimum curing temperature for the given raw material composition and this is found to vary marginally on curing period. 

An experimental program was carried out in order to investigate the usability of recycled coarse aggregate (RCA) concrete with and without ground granulated blast furnace slag (GGBFS). The RCA was derived from concrete having compressive strength of 47.6 MPa. Twelve concrete mixtures having various RCA (0-25-50-100%) and GGBFS (0-30-60%) replacement levels were designed with a water-to-binder (w/b) ratio of 0.50. Fresh concrete properties were observed through workability and slump loss. Compressive strength, tensile splitting strength, bond strength, ultrasonic pulse velocity, water absorption and density of hardened concretes were also determined at 7 and 28 days and the relations between physical properties and mechanical properties of RCA concretes with/without GGBFS were investigated. The RCA content significantly improved the tensile splitting strength of the concrete according to the compressive strength and the use of 60% GGBFS content in RCA concrete had a marginal increasing effect on the tensile splitting strength. The mixes containing 100% RCA was found to be noticeably beneficial in terms of the bond strength and the highest bond strengths were obtained with the use of 60% GGBFS content in RAC for all series at 28 days. However the lowest density and the greatest water absorption was obtained for RAC and an inverse relationship between the density and the water absorption ratio was determined.

Present work is devoted to a better insight into the identification of carbonation versus efflorescence formation in alkali-activated blast-furnace slag and investigates the relation between the chemical composition of the alkali-activator and the extent of the occurrence of these two phenomena. Obtained results showed that mixes of relatively lower alkali contents suffers not only from weak compressive strength due microstructural defects, but also from carbonation during the first few days. On the other hand, mixes containing relatively higher alkali contents strongly suffers from efflorescence formation in spite of their interestingly high compressive strengths. Carbonation during the first few days can partially neutralize the alkali content of the surface layers of the material which in turn significantly affects the activation mechanism leading to the formation of binding compounds of lower degree of Si substitution with Al in the molecular structure.

One kind of the irregularities in structures, with considerable effect on seismic performance, is setback in elevation that causes large damage especially in the vicinity of the irregularity. The main objective of this research is to propose and develop drift based index to estimate damage to Reinforced Concrete Moment Resisting Frames (RCMRFs) with setback. For this purpose, first, inelastic dynamic time-history analysis is performed on several frames with different types of setbacks subjected to various earthquake records and damage to them is computed by the Park-Ang damage index. Then two relations between the damage and drift are derived by applying irregularity indices to account for setback effects. It is shown that the proposed damage indices are capable to estimate the damage index of setback frames.

In this study, a comparison is made between force and displacement controlled non-linear FE analyses for an RC beam in flexure with partially developed steel bars. An FE model with slightly unsymmetrical reinforcement was analyzed by applying two-point loading using both force and displacement controlled methods. The responses obtained using ANSYS-13 were validated against available experimental data. Combined comparative display of flexural response of the beam using force and displacement controlled analysis, that has least been addressed in the literature, is given here. Study choses large-deformation-nonlinear plastic analysis scheme, discrete modeling approach for material modeling and program-chosen incremental scheme following Newton-Raphson method. The results show that displacement controlled approach is efficient in terms of time saving and less disk space requirement along with the ability to give falling branch of load-deflection response, if element displacement capacity still exists. Moreover, it gives an early estimate of the load carrying capacity of the structural element along with suitable values of convergence and non-linear solution parameters. However, for a beam with unsymmetrical detailing, force controlled analysis method seems to yield more realistic and practical results in terms of mid span deflection and beam cracking behavior compared with assumed symmetric displacement controlled technique. It also gives true fracture prediction at ultimate load level, which is not true for the displacement controlled method as the computer code forces the model to maintain equal displacements at two load points, falsely increasing the capacity of the beam.

This paper presents a comparative numerical research on the overall seismic behavior of RC frames with different types of rebars (normal versus high strength rebar). A nonlinear numerical model is developed and is validated using experimental results. Comparing the numerical and experimental behaviors shows that the developed model is capable of describing the hysteretic behavior and plastic hinges development of the experimental RC frames with various strength longitudinal steel bars. The validated model is then used, considering the influences of axial load ratios and volumetric ratios of longitudinal rebars of column, to investigate the effects of reinforcement strength on the overall seismic behavior of RC frames. The simulation results indicate that utilizing high strength reinforcement can improve the structural resilience, reduce residual deformation and achieve favorable distribution pattern of plastic hinges on beams and columns. The frames reinforced with normal and high strength steel bars have comparable overall deformation capacity. The effect of axial load ratio on the energy dissipation, hysteretic curves and ultimate lateral load of frames with different strength rebars is similar. In addition, increasing the volumetric ratios of longitudinal rebars can increase the ultimate lateral load of frame and improve the plastic hinge distribution of frame.

This study investigated the structural behaviors of reinforced concrete shear walls containing opening and slab. A series of three half-scale shear wall specimens were tested: a solid wall (WS-Solid), a wall with opening and slab (WS-023), and a wall with opening but no slab (WB-0.23). Using the experimental results, the reduction in the load-carrying capacity of the wall due to the loss of cross section was evaluated. Its contribution to the moment resisting capacity of the total system of coupling elements and its structural behavior was also examined. The results of experiments conducted on the WS-0.23 specimen with artificial damage due to installation of the opening, showed that the load-carrying capacity of the wall decreased as a result of the opening. It is apparent that the influence of cutting reinforcing bars and reduction of effective sectional area lead to early first yield of the reinforcing bars before the allowable limit of the drift ratio of the shear walls is reached. This decrease in the load-carrying capacity of the shear wall because of installation of openings is significantly different from the results of previous studies. This is because slabs and the remaining wall function as coupling elements for the shear wall. The contribution of slabs and residual wall to the lateral load resisting system was investigated via an empirical test and finite element analysis. During the experiment, a U-shaped critical section of coupling slab was observed and its effective width and the total length of the critical section examined. The critical section of coupling slab that functions as a coupling element for shear wall varied marginally from the results of previous studies. The results of the analysis conducted show that slabs and residual walls contribute approximately 30% to the lateral load resisting system.

Colored self-compacting mortar (C-SCM) is a novel cementitious product that has been recently used in decoration and rehabilitation and has improved aesthetic quality of architectural constructions. C-SCM is susceptible to strength decrease due to excessive pigment presence in the mixture. Optimum pigment content with respect to color intensity and mechanical performance is an important matter that should be determined to prevent mortar failure after construction. In this research, two inorganic pigments in production of colored self-compacting mortar were utilized. The impact of titanium dioxide (TiO2) and iron hydroxide (FeO(OH)) contents on behavior of C-SCMs were investigated in white and gray cement matrixes. Experiments included measurements of compressive strength of mortar cubes and cylinders, flexural strength and colorimetric properties. Analyses on compressive and flexural toughness were applied, as well. It was concluded that pigment content in mix design of colored self-compacting mortar could be optimized with regard to color quality in surface and mechanical strength of the product. Results implied that 5 and 2% of titanium dioxide were the saturation points of color and strength respectively and iron hydroxide at 10% was unsurpassed in C-SCMs containing white cement. Application of both pigments in gray SCMs caused the saturation points of color and strength to occur at 10 and 2%, respectively.