International Journal of Civil Engineering
Volume:15 Issue: 8, Dec 2017

In this work, a special type of bracing systems, called the “Drawer Bracing System (DBS)”, is proposed for improving the seismic performance of concentrically braced frames. DBS is a passive energy dissipating device belonging to the class of metallic yielding hysteresis dampers and is used to control and enhance the structure’s seismic performance. It was developed at the K. N. Toosi University of Technology (KNTU) and was tested in a half-scale braced frame. DBS is made up of three parallel plates that are joined together via transfer plates. The transfer plates are at right angle to the parallel plates and undergo minor axis bending. The parallel plates help the system remain elastic, control the global buckling of the system and provide the required strength and stiffness to transfer load to the energy dissipating components of the system. Energy dissipation occurs due to inelastic behavior of the transfer plates. Height, thickness, width, pitch, shape and connectivity of these plates may be varied to get the desired performance characteristics such as strength, stiffness and ductility. This paper provides an overview of the proposed system, the half-scale tests setup and the corresponding measurement results. Moreover, nonlinear finite element analysis of the system was carried out in ABAQUS to evaluate its seismic performance. Experimental and analytical results show that the hysteresis loop of this passive energy dissipating device is wide, symmetric and very stable, corresponding to a significant amount of energy absorption due to buckling elimination in steel braces.

The fresh properties of Self Compacting Concrete (SCC) might be more susceptible to quality and quantity changes of ingredients than conventional concrete because of a combination of detailed requirements, more complex mix design, and inherent low yield stress and viscosity. In spit of the low robustness of SCC, there are a few methods available to assess the SCC robustness that the accuracy of these methods has not been fully agreed. The current study provides an index for SCC robustness based on the rheology parameters. Thus, an experimental program was undertaken to evaluate the robustness of eight selected SCCs. For doing this, water content of each SCC was changed slightly and their fresh and hardened properties were measured. The results indicated that the length of rheology parameters curve due to variation of mixing water is able to assess the SCC robustness that is comparable with combined performance based on the workability tests changes. According to this index, the robustness of SCC increases about 10% using air-entraining admixture (AEA) and decreases considerably by reduction the paste volume (up to about 5 times). In addition, the most appropriate single workability test to assess the robustness is sieve segregation test. Moreover, the scattering of compressive strength results show that there is a level of robustness in fresh state that after that the scattering of results in hardened state can be affected.

One of the frequent aspects of lawlessness at signalized intersections is red light violation (RLV). In addition to adverse effects on intersection safety, RLV can cause delay in the startup of the vehicles in the competing phase, defined as the green flow in this study. In this research, a video camera was used to collect the required data from intersections to investigate the adverse effect of RLV in the city of Esfahan, Iran. Then, by assigning a cellular network to the conflict points of the vehicles path in successive phases, the vehicles arrival times to these cells were measured and the imposed delays to the green flow were measured. The results of this study showed that the behavior of drivers in the green flow, the time passed into red interval, and the presence of an all-red interval are the prominent factors affecting the delay caused by RLV. Furthermore, in the absence of all-red intervals a delay in the range of 1–4.5 s was inflicted on the subsequent competing green phase. Results of the study also showed that the amount of delay increased substantially when a RL violator was not permitted to precede through the intersection by the green flow vehicles.

A highly accurate nonlinear analytical algorithm to simulate the behavior of reinforced concrete (RC) columns under monotonic biaxial bending moment and axial loading is proposed. In the proposed algorithm, the nonlinear behavior of confined and unconfined concrete elements as well as steel elements is considered, and the column is discretized into two macro-elements located between the pseudo-plastic hinges at critical sections and the inflection point. The critical sections of the column are discretized into a number of rotary oblique fiber elements (ROFEs) and the neutral axis (N.A.) position of each section in each step of loading is searched automatically using a proposed “4-rotations and 2-translations” search model. The ROFEs remain always parallel to the N.A. of the sections and make a uniform stress distribution along each ROFE in each section. Consequently, the variations of stress across each fiber are quite small which increase the accuracy of the calculation, while the number of elements (fibers) is relatively small compared to those of the fixed rectangular finite element (FRFE). This research shows that there is a better agreement between the simulated results using ROFE discretization and experimental results performed in the full-scale RC columns than when the FRFE discretization model is employed. The application of the component effect combination method is also compared with the proposed simultaneous direct method.

The moisture transfer coefficient (MTC) is an important parameter utilized in modeling of moisture ingress into concrete. Test methods for estimating the MTC are generally performed using time-consuming combined experimental–numerical procedures. This paper presents a simple and practical method for the determination of the MTC using only water absorption test results. In this regard, a comprehensive nomograph was constructed based on finite element (FE) analysis of moisture transfer which relates the MTC to the water absorption measurements of concrete specimens. To validate the proposed method, eight concrete mixtures were prepared and their MTCs were obtained using the proposed nomograph and water absorption measurements after 1 and 4 h of immersion. Using the estimated MTCs, a numerical model was applied to predict the water absorption. The subsequent water absorption data resulting from the FE model were compared with the laboratory test results at intervals of 8, 12, 24 and 72 h, with h standing for “hour”. An observed error level up to 5% confirmed the validity of the proposed method.

Construction contractors do not have a clear understanding of sustainability, especially in developing countries. However, they welcome higher productivity as a determinant parameter in scheduling and financial success of construction project. Therefore, construction productivity improvement can be employed as an incentive to persuade contractors for implementing sustainability mechanisms in construction project. On the other hand, sustainability is a comprehensive concept which requires system thinking for implementation. Therefore, this study developed a qualitative System Dynamics model to contribute to measuring sustainability performance of construction project, considering contractors’ tendency to productivity. Sustainability performance is examined in three aspects of economic, social and environmental by introducing different subsystems and feedback loops. These loops formed based on experts’ opinions about causal links among the factors affecting construction sustainability and productivity. The findings provide a proper basis for both practitioners and researchers through illustrating the cohesion between productivity and sustainability.

Traffic simulation is a powerful tool for analyzing and solving several transportation issues and traffic problems. However, all traffic micro-simulation models require a suitable car-following model to show the real situation in the best way possible. Several car-following models have been proposed. An obvious disadvantage of the former models is the great number of parameters which are difficult to calibrate. Moreover, any change in these parameters creates considerable disturbances. In this paper, a car-following model was proposed using the Epsilon-Support Vector Regression (ε-SVR) method whose output is the acceleration of the following car. Radial Basis Function was used as the kernel of the ε-SVR method, and the model parameters were tuned using the Grid Search method. The best values for the parameters were obtained. Furthermore, linear scaling in the interval [−1, 1] was used for both the training and testing input data, and the method was proven to more accurate than the case where no scaling was used. Accordingly, a car-following model with the mean squared error equal to 0.005 and the squared correlation coefficient equal to 0.98 was proposed using the function estimation method through the ε-SVR method. Finally, the ε-SVR output was compared with the results of the well-known car-following models, including Helly linear model, the GHR model, and the Gipps model. It was shown that, when using the scaling and parameters tuning techniques, the proposed method was more accurate compared to all three models mentioned above. Moreover, a function fitting Artificial Neural Network was run for this purpose and the outputs showed that the result of the ε-SVR method is better than that of the function fitting method by the proposed ANN. Implementing a microscopic validation of the proposed model showed that it can be used in the drivers’ assistance devices and other purposes of intelligent transportation systems.

In recent times, bus arrival time prediction (BATP) systems are gaining more popularity in the field of advanced public transportation systems, a major functional area under intelligent transportation systems. BATP systems aim to predict bus arrival times at various bus stops and provide the same to passenger’s pre-trip or while waiting at bus stops. A BATP system, which is accurate, is expected to attract more commuters to public transport, thus helping to reduce congestion. However, such accurate prediction of bus arrival still remains a challenge, especially under heterogeneous and lane-less traffic conditions such as the one existing in India. The uncertainty associated with such traffic is very high and hence the usual approach of prediction based on average speed will not be enough for accurate prediction. To make accurate predictions under such conditions, there is a need to identify correct inputs and suitable prediction methodology that can capture the variations in travel time. To accomplish the above goal, a robust framework relying on data analytics is proposed in this study. The spatial and temporal patterns in travel times were identified in real time by performing cluster analysis and the significant inputs thus identified were used for the prediction. The prediction algorithm used the Adaptive Kalman Filter approach, to take into account of the high variability in travel time. The proposed schemes were corroborated using real-world GPS data and the results obtained are very promising.

A ten storey steel office building, designed for a low-risk zone under the former Italian seismic code and in line with Eurocodes 1 and 3, is considered as test structure. More specifically, the dynamic response of the test structure in a no fire situation is compared with what would happen in the event of three fire scenarios, on the assumption that the fire compartment with a uniform temperature is confined to the area of the first (i.e. F1), fifth (i.e. F5) and tenth (i.e. F10) level, with the parametric temperature–time fire curve evaluated in line with Eurocode 1. For each fire scenario, two retrofitting structural solutions are examined to upgrade the fire damaged test structure, by inserting diagonal steel braces with or without viscoelastic dampers along the perimeter of the level where the fire compartment is hypothesized only. Frame members are idealized by a bilinear model, which allows the simulation of the nonlinear behaviour under seismic loads, while an elastic linear law is considered for diagonal braces. Finally, viscoelastic dampers are idealized by means of a frequency-dependent model obtained as an in-parallel-combination of two Maxwell models and one Kelvin model. Dynamic analyses are carried out in the time domain using a step-by-step initial stress-like iterative procedure, assuming time histories of wind velocity, based on an equivalent spectrum technique, and artificial accelerograms, whose response spectra match those adopted by Italian seismic code. Results highlight the reliability of the VEDBs to control discomfort and deformability thresholds, under wind loads, and damage and buckling thresholds, under seismic loads, especially when F1 and F5 fire scenarios are considered.

This paper presents an investigation of crack control in the large-area concrete slabs of terminal T2 of the Nanjing LuKou International Airport. The design and construction of large-area slabs established with a 170-m-long deformation seam at this terminal posed a design challenge. The analysis and control of the thermal stress was also important and presented various difficulties. This paper presents a basic distribution of the floor’s temperature stress based on analysis with the finite element method (FEM). According to the FEM analysis, the maximum values of the tensile stress are between 2 and 3 MPa in most regions of the first slab. The top floor and shear wall should receive additional attention with regard to design and construction. Furthermore, field monitoring was also conducted using an advanced basalt fiber-optic sensor. The results of this monitoring were validated using data obtained from traditional strain gauges. The monitoring data indicated that the maximum value of the tension strain was 400 με in the #3 bar and #4 bar of the first slab. Then, the shrinkage was increased, and the maximum value of the deformation was recorded as approximately −450 με. Throughout the theoretical calculations, the shrinkage stress was found to exhibit a maximum of 1.5 MPa at approximately 10 days, which means that the section had achieved a safe state. The internal stress distribution state was analyzed, and the crack-control measures were validated.