International Journal of Civil Engineering
Volume:17 Issue: 7, Jul 2019

The flexural performance and failure modes of concrete beams, strengthened with near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips were investigated. For this, reinforced concrete beams (150 × 250 × 1400 mm) were cast, and cured for 28 days, then strengthened with NSM CFRP strips at varying numbers (1–3), lateral spacing (50–100 mm), and embedment lengths (150–450 mm). The impact of staggering of NSM CFRP strips upon strengthening efficiency was tackled, as well. The flexural mechanical response, strain in strips at failure, and cracking and failure modes were evaluated for all concrete beams under a four-point loading test setup. The findings indicated that inserting NSM CFRP strips at a certain lateral distance from the main steel bars prevented end-cover peeling-off. Furthermore, staggering NSM CFRP strips contributed to increasing the residual flexural capacity and toughness of strengthened beams by as much as 30 and 51%, respectively, although it led to a slight reduction in their ductility. In general, the present study confirmed the findings of different literature works with regard to the effect of key repair parameters using NSM CFRP strips.

This paper focuses on the earthquake performance of St. Konstantinos church that was damaged during 1995 Kozani earthquake. The structural elements that suffered the most damage were the main longitudinal exterior masonry walls, which included a considerable number of door and window openings. Initially, a numerical study is performed to determine the stiffness properties of representative simple masonry wall arrangements that included combination of openings. Based on the findings of this preliminary study, a three-dimensional (3-D) numerical simulation of the St. Konstantinos church was built. An analysis of the seismic response was next performed where the masonry walls were represented by linear “beam type” frame elements. The recordings of the ground acceleration that were obtained during the earthquake at a close distance from the church were utilized. The deformation levels obtained from this 3-D seismic analysis are used next, to approximate the earthquake performance of masonry walls through a more refined two-dimensional (2-D) FEM representation. These linear simulation results are utilized to predict the development of flexural or shear limit-state conditions for the exterior masonry walls. It was verified that the observed damages are in agreement with such predictions. The 2-D numerical investigation was extended to include a non-linear simulation of the observed behaviour utilizing either a Mohr–Coulomb or a modified von Mises failure envelope. Again, the observed damage of the masonry wall was approximated reasonably well by these non-linear numerical predictions. A retrofitting scheme which included the construction of internal reinforced concrete jacketing was also briefly presented and its beneficial result in the structural performance was verified.

This research focuses on the evaluation of the seismic response of three doubly symmetrical RC wall structures having three height regimes and subjected to a series of bi-directional ground motion recordings. The recorded strong ground motions are rotated in a clockwise direction and the effects of this procedure on several engineering response measures (e.g., wall-bending moments, wall shear forces, and storey drifts) are evaluated. The three doubly symmetrical RC wall structures are designed according to the current Romanian seismic design code for a peak ground acceleration of 0.25 g. The strong ground motions used in this study consist of five pairs of recordings from the Vrancea intermediate-depth earthquakes of 1977, 1986, and 1990 and from the Erzincan and Aigion earthquakes in Turkey and Greece. The investigations show differences between the response measures as a function of the orientation of the strong ground motion horizontal components and significant differences between the responses of each individual structure, as well. Thus, the maximum response obtained from the rotation procedure can be regarded as dependent on both the ground motion characteristics and on the ground motion recording, as well.

There are two common intensity measures (IM), i.e., the peak ground acceleration (PGA) and the spectral acceleration (Sa), for earthquake waves. PGA is a simple peak value of wave, while Sa considers more complex spectral characteristics. And it is necessary to identify which one is suitable for evaluating the seismic vulnerability of high-speed railway (HSR) bridges rapidly developed in the world. A finite element model of a (48 + 80 + 48)m continuous girder HSR bridge with track structure was built by OpenSEES software, and was calculated via an incremental dynamic analysis using both PGA and Sa. The seismic fragility curves of bridge and track components were developed by comparing the seismic demand and capacity of components. The comparison results, respectively, using PGA and Sa, show that both PGA and Sa are suitable for evaluating the seismic vulnerability of HSR bridges, and the using of PGA obtains more conservative fragility curves. Those severely nonlinear components, such as the sliding layer and the sliding bearings, etc., do not have constant local natural vibration periods and their seismic responses are not sensitive to the spectral characteristics of earthquakes. The dispersion of engineering demand parameters (EDPs) using PGA is larger or less than that using Sa for those severely nonlinear components. However, the dispersion of EDPs using PGA is always larger than that using Sa for those linear or slightly nonlinear components.

The classic methods of structural design based on trial-and-error are generally highly iterative and computationally intensive, especially in a tall building consisting of thousands of structural members. This paper presents a closed-form solution for a minimum weight design problem which may be used at the early-stage design of a high-rise and slender structure. Before considering the weight-based problem, an intervening optimization formulation is introduced in advance which for a fixed amount of material presents an optimal pattern for its distribution. The obtained pattern is then used in the main problem, in which the total weight is considered as the objective function while satisfying the peak lateral deflection constraint and some practical requirements. The flexural stiffness in its general form is selected here as the design variable, so the proposed method is not restricted to a particular system, and any structural system may be addressed. A braced-tube 61-storey building example is presented to be designed based on the proposed technique to illustrate the effectiveness and practicality of the method.

In this paper, the feasibility of using nanoglass as a partial replacement of cement in combination with fly ash was investigated. Three concrete mixtures made with fly ash and nanoglass as cement replacements were studied as a preliminary investigation. The first mixture contained 25% class F-fly ash (FA) and 0% nanoglass powder (NGP); the second mixture had 12.5% class F-FA with 12.5% NGP; while the third mixture had 0% class F-FA, with 25% NGP. In all the mixtures, the water-to-cementitious (w/cm) ratios were kept constant at 0.42. Fresh properties of each mixture were tested, which included air content and workability. Expansion due to potential alkali–silica reaction (ASR) was also tested, as well as mechanical properties such as compressive strength, tensile strength, and flexural strength. It was observed that the increase in NGP content beyond 12.5% in the presence of 12.5% class F-fly had a negative effect on the concrete fresh and mechanical properties. Overall, the addition of NGP enhanced the mechanical properties of the concrete, and the expansion due to ASR is less than 0.1% which is the threshold value.

A shield tunnel can be damaged by shield shell extrusions, such as shield tunnel floating, which may cause contact (even a squeezing action) between the shield tunnel and shield shell. To fully analyze this problem, a detailed 3D-finite element model (FEM) of a shield tunnel under the effect of a squeezing action in the shield tail, soil pressure, jacking force, and grouting pressure, was established by applying a plastic-damage constitutive model of concrete. A full-scale test of three segment rings was conducted, and the test results verified the feasibility of the constructed FEM. In this study, different squeezing positions and deflection angles of the shield shell were analyzed. The results indicated that the area squeezed by the shield shell experienced the most damage, and the tensile damage to a segment reduced gradually as the squeezing position approached the circumferential seam. The damage range gradually increased with the increase in deflection angle. The effect of the squeezing position of the shield shell on the bending moment was larger than the effect of the deflection angle on the bending moment. However, the effect of the squeezing position and that of the deflection angle on the shear force were the same.

To simulate response of concrete members and structures, comprehensive description of concrete behavior is required. This paper presents two groups of models that could be used to simulate behavior of concrete in tension for finite element modeling. The first group of models is based on stress–strain relationships and the second is based on stress–displacement relationships. Six relationships available in literature are investigated to model the response of plain concrete struts of various shapes and the behavior of reinforced concrete frame. Three of these relationships define tension in terms of stress–strain, whereas the other three describe tension in terms of stress–displacement. Comparing model estimates with results from experiments on plain and reinforced concrete members, it is concluded that tensile behavior of concrete can be represented well using stress–strain relationship. Modeling tensile behavior of concrete based on stress–displacement relationships can simulate response of these members, too, but not as well. The stress–strain relationship given by Tsai is the best option to simulate tension in concrete compared to the other stress–strain relationships and stress–displacement relationships considered in this study.

The authors proposed an innovative concrete shear wall, a concrete shear wall with a single layer of web reinforcement and inclined steel bars. This arrangement of inclined steel bars was designed to enhance the wall’s seismic performance. The dynamic behaviours of mid-rise concrete shear walls, each with a single layer of web reinforcement and inclined steel bars, were investigated in the paper. Four mid-rise shear walls, each with a single layer of web reinforcement, were tested in this project. The web reinforcement and the arrangement of the inclined steel bars were taken as major test variables. The dynamic characteristics and responses of all specimens at different loading stages were determined experimentally, and a comparison of failure modes was performed. The earthquake response time history analysis of each specimen was also conducted using the finite element software ABAQUS. Based on test, the dynamic characteristics, dynamic responses and failure mode of each model under elastic and elastic–plastic deformation stages were compared and analysed. The results show that the configuration of inclined steel bars can effectively improve the seismic capacity and decrease the earthquake damage of mid-rise concrete shear walls with a single layer of web reinforcement.

Contract time is the maximum time allowed in the contract for the completion of the project scope of work. The allowed time must be enough for adequate completion and yet not too long that it delays the use of the project. The current practice of determining contract time relies heavily on completed plans and specifications. However, there is always the need to come up with contract time at different project phases when the plans and specifications are not yet complete. The objective of this research is to evaluate a conceptual method for determination of contract time using linear regression and the predictive quality of such method based on different project types. A predictive conceptual method will serve a purpose, especially when there is not enough time or information to develop a detailed schedule. The development of a linear regression based on Bromilow’s Time–Cost (BTC) model could enhance state department of transportation (DOT) ability to make informed decisions on project feasibility and contract time. The ability to make such decision could save the agencies time and money. Based on the projects evaluated, the findings indicate that contract value (amount paid at completion) alone is not a good indicator of the contract time. The research suggests that a better predictor of contract duration could be arrived using standardized project types. In addition to cost, such classification will include project dimensions such as construction type, system type, material type, project location, complexity category, traffic control category, environmental assessment, and other factors.

In this study, the effect of various pre-exposure loadings on chloride penetration in concrete beams, reinforced with both normal black and epoxy-coated bars, was experimentally investigated. In-service static and fatigue loads (around 30–35% of the designed loading capacity) were applied to the RC beams before they were exposed to a designed chloride wetting/drying cycles, simulating the seawater attacks at the tidal zone, for about 1 year. At the end of the simulated seawater exposure, the chloride profiles in the uncracked and cracked concrete cover were measured. Apparent chloride diffusion coefficients and surface chloride concentrations were then estimated on the basis of the measured chloride profiles. Results indicated that the differences in initial concrete compaction, load-induced micro-cracks and visible cracks are the main factors affecting the chloride penetration and diffusion coefficients. Fatigue load-induced cracks resulted in increase in chloride penetration in specimens compared with those in unloaded and static loaded specimens with similar initial compaction.

Accumulating construction and demolition waste (C&DW) and the rather high hydration temperature of cement are two problems which affect the environment and mass concrete production, respectively. In this study, the effects of reactive MgO hydration and cement content’s role on the mechanical characteristics of C&DW aggregate concrete were evaluated for finding the suitable solution for solving the above-mentioned problems. In the experimental program, sand to cement ratios of 3 and 2.5 were considered (S/C) and the reactive MgO was 2–6 wt% of cement. Also, two types of experiments such as mechanical and chemical tests were carried out. The compressive strength test showed that by increasing the reactive MgO to 6 wt% of cement, the compressive strength of samples in the S/C of 2.5 is higher than the 3. Also, by increasing the percentage of C&DW aggregate from 30 to 60%, the water absorption of samples increases. In the field emission scanning electron microscopy (FESEM) analysis with cases of 2–6% MgO, 60% C&DW aggregate and S/C of 3, cracks were observed, while they were not detected in samples with S/C of 2.5. The X-ray diffraction (XRD) test, confirmed that the major peak of the patterns in almost every sample was related to calcite and with increase in the MgO content to 6%wt., tricalcium silicate was not formed in both samples with S/C of 2.5 and 3. This study confirm that using C&DW aggregate as concrete is practical for making green concrete and using MgO helps to reduce its hydration temperature.

Traffic assignment is the last stage of the classical transportation planning process in which, the travel demand of each O–D pair is allocated to the network links, and links’ flows are estimated. To solve such a problem, some assumptions should be made about travellers’ decision-making behavior. One of the most popular approaches in this regard is the deterministic assignment that assumes all drivers are fully informed about the condition of the network and they always select the best (usually the shortest) route. These assumptions do not thoroughly match to the reality. To deal with this problem, the concept of stochastic user equilibrium has been introduced. The conventional stochastic user equilibrium assignments models are typically based on random utility theory. In this paper an alternative approach for stochastic user equilibrium assignment called random regret theory has been used in which a random regret-minimization (RRM) model is developed. RRM considers the regret of an option just with respect to outperformed options and furthermore does not lead to a closed-form stochastic user equilibrium (SUE) model, though based on that a formulation of SUE is proposed in a variational inequality form. In this study the definition of regret is modified and based on that a closed form SUE model is developed. This model is examined by two network examples.

This paper aims to identify the sources of competitive advantage for contractors on international high-speed railway (HSR) construction projects, to help them understand these sources, and to provide an integrated way of orienting their competitive position by measuring these driving variables. Based on an in-depth literature review and case analysis, 24 initial variables were identified. Following the pilot study, experience mining was merged into knowledge management. Structural questionnaires, including 23 final variables, were then distributed to professionals from academia and industry. A total of 202 valid responses were received. Mean score ranking and exploratory factor analyses were conducted to reveal the relative important variables and the underlying groupings, respectively. In the last section, a case study with five international contractors was conducted to show the method for assessing their comprehensive competitiveness. According to mean score ranking, the variable “construction safety” was the most important, with a mean value of 4.25. Following an exploratory factor analysis, six underlying factors from the SCA dimension (including management ability, strategic capital, and social influence) and the TCA dimension (including technical skills, operational performance, and financing ability) were identified as significant underlying sources of competitive advantage for contractors on international HSR projects. This study provides an in-depth understanding of sources of competitive advantage for contractors on international HSR projects, and it helps them in precisely orienting their competitive position.

Self-consolidating concrete (SCC), despite its many positive advantages, increases the formwork lateral pressure of the mixture due to its high fluidity, leading to the increased cost of formwork construction in the in situ concrete structures. The thixotropy property, as the most significant functional feature including the effect of mixture proportions on lateral pressure, was selected to investigate the behavior of fresh concrete in the mold. In the present study, the thixotropy and formwork pressure characteristics (including maximum lateral pressure and pressure drop rate) of 15 SCC mixtures were investigated by considering a number of mixtures proportions variables including cement content, water-to-cement ratio, and mineral admixtures. In addition to studying the effect of these variables on the thixotropy level and the lateral pressure of the formwork, the relationship between the methods of measuring the thixotropy level (hysteresis methods, the area of structural breakdown, and the yield stress growth rate) was evaluated considering the mechanism of these methods. In this study, formwork pressure simulator device was used to measure maximum lateral pressure and lateral pressure drop rate. In addition, the effects of mixture proportioning variables on thixotropy and its relationship with the formwork pressure were studied. Using these indices, the ability to predict the behavior of concrete in the mold was investigated through modeling. The presented predicting model of the formwork pressure based on thixotropy value showed an acceptable correlation coefficient (R2 > 0.77).

In accordance with two different design methods including the technical specification for steel structures of tall buildings and the shear-bearing capacity method for infilled steel wall plates, two types of steel plate shear wall with unstiffened panels have been designed and constructed. All shear wall specimens are exposed to ultimate static monotonic and low horizontal cyclic loading conditions to determine their structural behaviors under an idealized severe earthquake event. The seismic performances of these two types of specimens are identified by the overall roof displacement angle, lateral stiffness, ductility, different distribution of horizontal force and overturning moment, and inclined angle of diagonal tension field. These two types of steel plate shear wall exhibit excellent seismic performance. However, the specimens with thin infill plate thickness of 1.1 mm perform better than the thicker specimens with plate thickness of 3.75 mm. In terms of serviceability performance, the experimental results exhibit that the thicker specimens designed by the technical specification tend to be more conservative. Their over-strength factor, strength assurance coefficient and drift angle are 4.98, 6.3 and 1/1335, respectively. However, the thinner specimens designed by the shear capacity method for shear panel yield the serviceability performance factors of 2.22, 2.71 and 1/407, respectively. It is important to note that design practice generally adopts the over-strength factor between 2 and 3, and the strength assurance coefficient is often designed for 3 and the maximum inter-story drift limit given by the design specification is 1/300. On this ground, it is apparent that the shear-bearing capacity method enables relatively more economical compared to the technical specification for steel structures.

Evaluating the environmental impacts of WWTPs and finding ways for wastewater reuse with minimum damage to our environment and human societies is a matter of vital importance. The objective of this study is to identify the critical sources of environmental impacts in Tehran’s WWTP using life-cycle assessment (LCA) method. Eco-Indicator 99 is selected to perform life-cycle impact assessment (LCIA) using SimaPro 7.0 software. Results show that application of biogas instead of natural gas can make a significant contribution in alleviating the environmental effects of Tehran’s WWTP (e.g., decreasing the negative impacts of fossil fuels about three times). Discharging the effluent into the surface water resources causes considerable damages to the quality of these resources and should be prevented. Instead, using the effluent for agricultural purposes in south of Tehran is a more eco-friendly practice especially from an eutrophication perspective (4% of the previous scenario). In general, the results obtained from implemented case study show that despite some shortcomings such as availability of sufficient and reliable data, LCA is an appropriate environmental system tool capable of streamlining the decision-making process in the wastewater treatment industry in Iran as well as fostering opportunities to achieve sustainability goals.

This research utilizes DrinC software and some codes developed in MATLAB software for calculating the drought indices and determination of trend of climatologic and hydrologic time series data using different nonparametric Mann–Kendall trend tests. The time series data used in this research include the minimum, mean and maximum monthly temperatures, monthly precipitation, and monthly flow discharge (from 1981 to 2012). These data are pertinent to the Dez watershed climatic and hydrometric stations in southwest Iran. Results of this research show that precipitation has no significant trend, but flow discharge has a decreasing trend. The trends of mean, maximum, and minimum temperatures are increasing in summer and autumn but decreasing in spring. In winter, the trend of minimum temperature is increasing, while the trend of mean and maximum temperatures is decreasing. Standardized precipitation index (SPI) and streamflow drought index (SDI) show that the number and intensity of short-term droughts (with 3 months time scale) are more than the number and intensity of long-term droughts (with 6, 9, and 12 month time scales). Correlation coefficient between SPI and SDI increases as the time scale is increased too.

Energy criterion is a simple and scalar quantity, so it has been employed by many researchers for the assessment of seismic behavior. Production and presentation of input energy spectra are effective steps for the employment of energy criterion in the seismic design of structures. Ninety-two pairs of horizontal components of Iranian earthquakes were used for this research. These records were divided into near-field and far-field, and in each field, soils categorized to types 1–3. Using nonlinear dynamic analysis, 92 inelastic spectra of relative input energy per unit mass were generated for a damping ratio of 5% and a ductility factor of 3. Then, for each category of records, a combined spectrum was produced at design level corresponding to 10% risk in 50 years. The evaluation of combined spectra led to the conclusion that the average value of combined spectrum in near-field is greater than that in far-field. In addition, the average value of combined spectrum is greater for softer soils. The corresponding period to the peak of combined spectrum in near-field is longer than that in far-field. The effect of soil type in near-field is more than that in far-field. For each field and each type of soil, a relation and its parameters have been proposed for the inelastic spectrum of relative input energy per unit mass.

The purpose of this paper is to study experimentally and numerically the dynamic response of a hollow core concrete slab due to a single pedestrian. To achieve this aim, a test structure consisting of six hollow core concrete elements of dimension 10 m × 1.2 m has been built. A finite element model of the structure based on orthotropic shell elements has been implemented. The accuracy of the finite element model has been assessed by reproducing numerically hammer-impact tests. For that, the experimental impact load has been imported to the finite element model. Very good agreements between experimental and numerical results have been obtained. Then, three different single pedestrian walking paths have been tested experimentally. Each of these paths has been reproduced numerically using four numerical load models taken from the literature. The results show that the four pedestrian loads give rather different numerical results regarding the amplitudes of the acceleration for each mode. In addition, a small change in the numerical parameters of the slab can give large differences in the numerical results. This shows that an accurate numerical modelling of a single pedestrian loading is not an easy task. The results show also that during transversal and diagonal walking paths, the vibrations due to the torsional mode of the slab can be higher than the ones due to the lowest bending mode.