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Strengthening the seismic deficient beam-column joints (BCJs) in reinforced concrete structures is mostly adopted to avoid any devastating consequences of high-intensity earthquakes. To evaluate the performance of BCJs against seismic action, experimental testing of BCJs under cyclic loading is a time-consuming and cost-intensive work due to the requirement of large-scale instrumentation and testing. This paper reports a study on the numerical and analytical modeling of the seismic behavior of BCJs built using normal concrete and retrofitted with ultra-high performance fiber reinforced concrete (UHPFRC). A computer simulation using the nonlinear finite element (FE) method was developed considering a concrete damage approach in modeling both types of concrete, i.e., normal concrete (substrate) and UHPFRC (overlay). The interface between the substrate and overlay was modeled as a cohesive element. The properties of this bonding interaction were experimentally evaluated based on the results of the push-out test. The simulation results benchmarked with the experimental data of a previously published study. It was found that the proposed FE model is in good agreement with the experimental behavior of seismically tested specimens in terms of global load–displacement, ultimate load, and damage evolution. In addition, the use of surface-to-surface cohesive elements played an important role in the bonding interface under cyclic loading. Additionally, an analytical model was developed to predict the shear capacity after retrofitting the BCJ. The results obtained by using the analytical model were consistent with the corresponding experimental values. Finally, a parametric study was carried out to examine the effects of the thickness of UHPFRC jacketing and longitudinal reinforcements ratio of the beam on the performance of the retrofitted BCJs.

This paper is intended to investigate the stress block for high strength concrete (HSC) using the finite element model (FEM) and analytical approach. New stress block parameters were proposed for HSC including the stress intensity factor (α1) and the depth factor (β1) based on basic equilibrium equations. A (3D) finite element modeling was developed for the columns made of HSC using the comprehensive code ABAQUS. The proposed stress parameters were validated against the experimental data found in the literature and FEM. Thereafter, the proposed stress block for HSC was used to generate interaction diagrams of rectangular and circular columns subjected to compression and uniaxial bending. The effects of the stress block parameters of HSC on the interaction diagrams were demonstrated. The results showed that a good agreement is obtained between the failure loads using the finite element model and the analytical approach using the proposed parameters, as well as the achievement of a close agreement with experimental observation. It is concluded that the use of proposed parameters resulted in a more conservative estimation of the failure load of columns. The effect of the stress depth factor is considered to be minor compared with the effect of the intensity factor.

Reinforced concrete buildings with moment-resisting frames comprising beam–column joints (without joint shear reinforcement) designed prior to introduction of seismic codes are shear deficient when subjected to seismic loading, thereby mostly fail in shear at the core of the beam–column joint. However, those designed to the new seismic codes may fail by flexural hinging at the interface of the beam–column joint due to the yielding of the beam reinforcement at the location of highest stress demand (usually the beam–column joint interface). The shear failure has been precluded through the provision of transverse reinforcement at the joint in new design and the use of carbon fiber–reinforced polymer retrofitting in old buildings. Plastic hinge formation at the interface of the beam–column joint is critical because of its penetration into the joint and its effect on bond deterioration. In this study, eight corner-external beam–column joint specimens of 1/3 scale of a typical moment-resisting frame, made without transverse reinforcement, were tested for monotonic and reversed cyclic test under displacement-controlled regime. The control specimens failed by flexural hinging at the beam–column joint interface. The experimental results have been validated using the finite element model. The specimens were retrofitted with unidirectional carbon fiber–reinforced polymer of different layers and different length. After retrofitting, the plastic hinge was relocated to the curtailment end of the carbon fiber–reinforced polymer. The relocation of the plastic hinge resulted in higher load capacity and ductility.

The use of concrete-filled stainless steel tubular (CFSST) members is relatively innovative and new. CFSST columns can be used for bridge piers, multi-story buildings and other supporting structures. However, a common mode of failure with these type of tubular composite columns is inelastic outward local buckling occurring at the column ends. Therefore, this paper presents the results of experimental, numerical and analytical investigations into the behavior of circular CFSST columns strengthened by carbon fiber reinforced polymer (CFRP) wrap and subjected to axial compression loading. The experimental investigation comprised three series of tests. The main variables tested were the diameter to thickness ratio of the stainless steel tube and the thickness of the CFRP wrap. 3D finite element models (FEMs) were developed for CFRP-wrapped CFSST columns using the ABAQUS software and were validated with experimental results. An extensive parametric study was carried out by using the validated FEMs. It was shown from the experimental and FEMs results that CFRP jacketing was highly effective in improving the axial load carrying capacity and axial shortening capacity of the CFSST columns. Finally, an analytical model based on the FE parametric study results was proposed to predict the axial load carrying capacity of the CFRP-wrapped CFSST columns.

The focus of this paper is to investigate the effect of column axial load levels on the performance of shear deficient reinforced concrete beam column joints (BCJs) under monotonic and cyclic loading. The problem of interaction between shear stress in BCJ and axial load on column has been addressed in this work by initially postulating a mechanistic model and substantiated by an experimental test program. This was achieved by conducting appropriate tests on seven BCJ sub-assemblies subjected to monotonic and reversed cyclic loading, with varying levels of the column axial load. Experimental results were further validated using a finite element model in an ABAQUS environment. The effect of variation of compressive strength of concrete was considered in a subsequent parametric study, in order to obtain sufficient data, and utilized to develop a new shear strength model for BCJs which includes influences of all the important parameters required to predict the shear strength of BCJs. The results showed that column axial load affects the seismic performance of BCJs significantly. Experimental results demonstrated that at initial stages of loading, increase in axial load enhances the shear capacity of the joint and reduces its ductility. However, when the column axial load/axial strength ratio increases to about 0.6–0.7, shear strength starts to decrease rapidly, leading to pure axial failure of the joint. The magnitude of axial load/axial capacity ratio also dictates the failure mode and development of crack patterns in BCJs. Results of reverse cyclic tests on BCJs showed that high value of axial load/axial capacity ratio increases the initial stiffness of BCJ but rate of stiffness degradation is accelerated after peak strength attenuation.

This study presents the buckling response of functionally graded (FG) “sandwich plate” on a viscoelastic foundation and exposed to hygrothermal conditions. An accurate solution is developed using higher-order shear deformation theory (HSDT), with only four unknowns being placed to reach the solution. The displacement fields first utilize an indeterminate integral accompanied by a sinusoidal shape function to simulate the transverse shear deformation theory. The foundation’s mathematical model followed the two-Pasternak coefficient model, with one more term being added to represent the damping effect. The sandwich plate is essentially composed of three layers. This study presented three different FG sandwich plate geometric analytical solutions regarding layer orders and composition. The equations of motion were generated according to Hamilton’s principle. Thereafter, the analytical solution was based on Navier’s principle to solve the buckling temperature of a simply supported FG sandwich plate seated on a viscoelastic foundation. This paper shows a parametric study of the effect of the damping coefficient along with the aspect ratio, moisture condition, power-law index, and temperature variation over the buckling temperature of the FG “sandwich plate” on the viscoelastic foundation.

The repair and strengthening of reinforced concrete members are very important due to several factors, including unexpected increases in load levels and/or the damaging impact of aggressive environmental conditions on structural concrete members. Many researchers have turned to using materials for the repair and strengthening of damaged structures or the construction of new concrete structural members. Ultrahigh-performance fibre-reinforced concrete (UHPFRC), characterized by superior structural and durability performance in aggressive environmental conditions, is one of the materials that have been considered for the repair and strengthening of concrete structural members. The repair or strengthening of concrete structures using UHPFRC needs a thorough knowledge of the behaviour of both the strengthening material and the strengthened concrete structure at service load conditions, in addition to an understanding of the design guidelines governing the use of such materials for effective repair and strengthening. In this study, the recent issues and findings regarding the use of UHPFRC as a repair or strengthening material for concrete structural members are reviewed, analysed, and discussed. In addition, recommendations were made concerning areas where future attention and research on the use of UHPFRC as a strengthening material needs to be focused if the material is to be applied in practice.

The paper presents an experimental and numerical evaluation of reinforced concrete (RC) columns strengthened with ultra-high-performance concrete (UHPC). Fifteen columns were tested under static eccentric loading. The variables considered in the experimental program are the thickness of UHPC and the loading eccentricity. A three-dimensional (3D) numerical model was developed using ABAQUS software and validated with the experimental results. The validated numerical model was utilized to develop additional results of the strengthened RC column considering UHPC strength as a variable. Finally, an analytical model was proposed to predict the failure load and moment for rectangular RC columns strengthened with UHPC. The results confirmed the effectiveness of UHPC jacketing to strengthen RC columns under eccentric loading. The degree of enhancement is proportional to UHPC jacket thickness and inversely proportional to the nominal eccentricity. The proposed analytical model accurately predicted the failure load and moment for rectangular RC columns strengthened with UHPC.

The population growth and harsh weather conditions in Saudi Arabia increase the demand for electricity due to the overwhelming usage of air-conditioning system for cooling during the excessively hot weather summer conditions. Therefore, the demand to produce efficient insulation materials for building construction has recently increased for energy and environment conservation, particularly with the recent increase in the electricity tariffs. In this paper, finite element analysis using ABAQUS software was used to determine the optimum geometry of holes for concrete bricks that would increase the thermal resistance of the wall, thereby reducing the consumption of electrical power. The analysis was carried out for 23 models with different configurations of holes for masonry concrete bricks. Regular and staggered cavities arrangements were analyzed. The conduction, convection and thermal radiation phenomena were considered for solid and hollow masonry bricks. The results demonstrated that 51% hollow ratio could reduce the average inner surface temperature \((T_\mathrm{i})\) of the concrete brick by \(7.18\,{^{\circ }}\hbox {C}\). For bricks with the same hollow ratio, it was observed that there is an effect of the shape of holes in reducing the thermal flow through the bricks, while the number of holes has a marginal effect on the average inner surface temperature \((T_\mathrm{i})\). Further, the staggered arrangement for circular holes has considerable effect in reducing \(T_\mathrm{i}\) for bricks with four cavities, while the rectangular cavities have negative impact on \(T_\mathrm{i}\). Moreover, for the models with circular and rectangular eight cavities, the staggered arrangement has an advantage in reducing \((T_\mathrm{i})\).

Extensive research work has been performed on shear strengthening of reinforced concrete (RC) beams retrofitted with externally bonded carbon fiber reinforced polymer (CFRP) in form of strips. However, most of this research work is experimental and very scarce studies are available on numerical modelling of such beams due to truly challenging nature of modelling concrete shear cracking and interfacial interaction between components of such beams. This paper presents an appropriate model for RC beam and to simulate its cracking without numerical computational difficulties, convergence and solution degradation problems. Modelling of steel and CFRP and their interfacial interaction with concrete are discussed. Finally, commercially available non-linear finite element software ABAQUS is used to validate the developed finite element model with key tests performed on full scale T-beams with and without CFRP retrofitting, taken from previous extensive research work. The modelling parameters for bonding behavior of CFRP with special anchors are also proposed. The results presented in this research work illustrate that appropriate modelling of bond behavior of all the three types of interfaces is important in order to correctly simulate the shear behavior of RC beams strengthened with CFRP.

Use of heavy fuel fly ash (HFFA) (diesel and cracked fuel) for power generation in Saudi Arabia has generated and accumulated large quantities of HFFA as a byproduct. In this research, HFFA is studied with the emphasis on the utilization of this waste material in concrete blocks and asphalt concrete mixes. Two types of mixes, one with low and other with high cement content, were studied for concrete blocks. Different mixes having varying percentages of HFFA (0% to 25%), as cement/sand replacement or as an additive, were studied. The performance of concrete blocks is evaluated in terms of compressive strength, water absorption, durability and environmental concerns. The results showed that blocks cannot be cast if more than 15% HFFA is used; also there is a marginal reduction in the strength of all the mixes before and after being exposed to the sulfate solution for a period of ten months. HFFA is studied in asphalt concrete mixes in two ways, as an asphalt modifier (3&5%) and as a filler (50%) replacement, the results showed an improvement in stiffness and fatigue life of mixes. However, the stability and indirect tensile strength loss were found to be high as compared to the control mix due to moisture damage, indicating a need of using antistripping agents. On environmental concerns, it was found that most of the concerned elements are within acceptable limits also it is observed that lower concentration of barium is leached out with the higher HFFA concentrations, which indicates that HFFA may work as an adsorbent for this leaching element.

This study proposes efficient exterior concrete walls (consisting of blocks, mortars, and plasters) to reduce the heat transfer to or from buildings for minimizing energy consumption due to air conditioning or heating processes. Different blocks were treated by partially or totally replacing coarse and fine aggregates with insulation materials. Mortars and plasters were also treated by partially replacing sand with certain insulation materials. A control block (without treatment) was also produced with three-row rectangular cavities to reduce the effective thermal conductivity. Experimental tests were performed to determine the thermal conductivity of blocks, mortars, and plasters, and to validate a developed three-dimensional model (using ANSYS-Fluent program). The model results showed a substantial increase in model accuracy (about 15%) by involving the estimation of radiation heat transfer in the block cavities. The thermal and economic performance of treated masonry walls showed that the optimal performance was obtained from a wall having volcanic scoria-treated blocks (200-mm thick) and 15% vermiculite-treated mortar (10-mm thick). The thermal performance was enhanced by 15% and 318% (for thermal resistance increase) and 13% and 76% (for heat flux reduction) more than those of the control and market walls, respectively. Adding 15% vermiculite-treated plaster (2 × 15-mm thick) to the wall enhanced the thermal performance remarkably. The total cost of the improved wall (having the highest thermal resistance) was reduced by 1.39 and 3.67 times over the control and market walls (Dhahran, Saudi Arabia), respectively. This improved wall is a promising candidate for exterior walls in residential and industrial buildings.

The aim of this research was to reduce the demand for air conditioning in buildings by minimizing the heat flow from outdoor environment to the interior of building envelopes (walls and roofs). Hence, a finite element model (FEM) was developed to find out the optimum geometry of cavities and their layout in masonry concrete blocks in order to reduce the thermal flow of heat and the results were compared with that of hollow blocks available in the market in terms of thermal insulation. Results of the simulation were promising and indicated that the new “optimum” designed geometry of hollow blocks was much better than the hollow blocks available in the market. Thereafter, some insulation materials were utilized in the concrete mixtures to produce hollow masonry concrete blocks to reduce the thermal conductivity through wall elements. Experimentally, the results of the new block with optimum geometry without the insulation materials showed improved thermal insulation by as much as 71% compared to other designs of hollow blocks including those available in the market. The thermal resistance of concrete and masonry blocks with the insulation materials (perlite, rubber and polyethylene) was enticing and significant. The newly developed optimum design of masonry concrete block with and without the insulation materials satisfied the ASTM C129 requirements for non-load bearing walls in terms of strength and absorption and was considered as medium weight (without insulation material) and as lightweight (with insulation materials) masonry hollow blocks. Results of this comprehensive investigation also indicated that the thermal conductivity could be reduced by up to 40% compared to that of the conventional blocks available in the market. Therefore, it is recommended that these optimum designed blocks be utilized by the construction industry in order to reduce the amount of energy used for the air conditioning as well as the carbon footprrint.

The load-carrying capacity of an eccentrically loaded reinforced concrete column affected by corrosion of reinforcement will progressively decrease with time due to the buildup of corrosion-induced damage in the form of loss of reinforcement area, cracking and spalling of concrete cover. Due to the complexity of corrosion problems, a probability-based assessment of failure, instead of a deterministic approach to ascertain safety, is prudently more appealing. An attempt has been made to propose a method for computing probability of failure of corroded eccentrically loaded columns using Monte Carlo simulation (MCS) of a proposed limit state safety function based on a time-dependent strength prediction model for the residual strength. The MCS covers a large number of possible combinations of all governing parameters related to strength within their prescribed distributional characteristics. The results show that MCS can be used to estimate probabilities of failure, and that the corrosion current density and the ratio of eccentricity of the applied axial load to the depth of the section, e/h, are the two significant factors that affect the probability of failure at a prescribed corrosion period the most.

Carbon fiber-reinforced polymer (CFRP) sheets and plates are now being extensively used as retrofitting/strengthening system, due to high strength, low weight, corrosion resistance, and ease and speed of application. Structures with very low-strength reinforced concrete columns, constructed during the early 1970s and 1980s, are rampant in many countries. These structures are prone to collapse during a seismic event. It is important to investigate if these low-strength concrete columns can be made safe by CFRP sheet strengthening. An experimental and numerical investigation conducted on short circular low-strength concrete column is presented. The results of this study showed that the confinement equations for concrete columns as per ACI and CSA codes give erroneous results for these columns. The CSA code equations require satisfaction of certain constrains, which are not applicable to such columns. Control specimen (unconfined specimens) results showed that both CSA and ACI equations overestimate the ultimate loads of low-strength RC columns by an order in magnitude. For CFRP-confined specimens, the ACI and CSA code equations overestimate the strength by about 13% and 24%.

Post-tensioned single-cell concrete box girders of variable depth are used in continuous bridges to achieve both economy and aesthetics. In this paper, the minimum prestressing for a given two- or three-span continuous bridge deck profile is achieved through a constrained optimization procedure using linear programming in conjunction with gradient method of optimization. The constrained nonlinear problem is solved by transforming it to a linear one by introducing a new design variable which proportions long (full length) and short tendons. A gradient search technique is used to solve iteratively the optimization problem. The design variables include interior to exterior span ratio (for three-span), the depth profile of the cross-section, tendon profile, and prestressing force. The total cost of the member is taken as the cost of structural materials (concrete and prestressing steel), excluding the cost of formwork. The design constraints are the prescribed limits on the allowable stresses, ultimate strength, and serviceability requirements as per ACI 343R-95. A purpose-built computer program has been developed to readily determine the optimum prestressing for a given bridge deck profile. From solutions of a number of hypothetical bridge girders using AASHTO H20 bridge loading, several useful results related to design are obtained. Results show that for a symmetrical three-span and two-span continuous bridge girder, the optimum prestressing consists of an optimum arrangement of both long and short tendons, and for a three-span girder of prescribed length, the optimum design is attained at an optimum ratio of interior to exterior span with 1.35 to 1.45.

The spiral reinforcement is a very common technique used for reinforcing columns in active seismic regions due to its high ductility and high ability of energy absorption. This paper presents a nonlinear finite element analysis of high-strength concrete confined with opposing circular spiral reinforcements. The results are compared with tested scaled concrete columns made with opposing spirals under monotonic axial loads. The developed model is used to investigate the effect of spiral spacing, γ (ratio of the core diameter to the whole cross section diameter) and compressive strength on behaviour of circular spiral reinforced concrete column confined with opposing spiral reinforcements. The results of the parametric study demonstrated that for the same spacing between spirals and same strength of concrete, increasing γ will result into increasing the failure load of the column. It is also concluded that the ductility of the studied columns is not affected by changing the value of γ.

The residual strength of corrosion-damaged eccentrically loaded columns is presented along with a strength-prediction model developed on the basis of a substantial amount of test data generated from the testing of 48 specimens under eccentric axial loading, 36 of which were subjected to accelerated corrosion to induce various degrees of corrosion damage. The test variables included two different cross sections, two different diameters of longitudinal steel, and different corrosion periods. The proposed approach for an estimation of residual strength involves two steps: first, the strength is calculated by conventional mechanics using only the reduced area of steel after metal loss from corrosion, and then this value is reduced by multiplying with a proposed reduction factor developed through a multi-level regression of test data to collectively account for all other corrosion-damage effects. The accuracy of the proposed method has been verified by comparing results with available test data.