International Journal of Civil Engineering
Volume:10 Issue: 4, Dec 2012

Development of simplified procedures for estimating the seismic-induced demands in different components of building structures is an essential element in their performance based seismic design. The nonlinear static procedures (NSPs) proposed by design codes do not lead to reliable results especially for tall buildings. They generally provide inconsistent estimates of inelastic seismic demands, especially for the top floors due to their inabilities in considering the higher modes effects. A number of enhanced NSPs have been proposed in recent years to overcome the shortcomings of conventional methods. In this paper, a new enhanced pushover procedure is proposed which is based on the envelope of the structural responses resulting from two separate pushover analyses as a combination rule. Also, the suggested pushover analyses are performed using a newly proposed modal load pattern, i.e., the Modal Spectra Combination (MSC), and the ASCE41-06 required first mode load pattern. The MSC load pattern is consist of a number of mode shapes combined with appropriate weighting factors that depend on their modal participation factors, modal frequencies and design spectral values. A number of 2-D steel moment resisting frame models with different number of stories are used to investigate the efficiency of the proposed method. The inter-story drifts and the maximum plastic beam moment and curvature responses are used as a measure to compare the results obtained from the nonlinear time-history analyses (NL-THA) and some other NSPs. Appropriate scaled earthquake records, depending on the site soil type, are used for nonlinear dynamic analyses and determining the exact response of the structural systems. It is shown that the application of the proposed method leads to acceptable results for steel moment resisting frame systems in comparison to other available enhanced NSPs. The OpenSees program is used for numerical analysis.

Strut-and-Tie Model (STM) can be used to model the flow of compression within a concrete strut. Concrete struts are formed in various shapes such as prismatic or bottle-shaped. In order to study the behavior of concrete struts, a series of simple tests were performed. Eighteen reinforced concrete isolated struts with compressive strength of 65 MPa were tested to failure under point loading in the plane of specimens. The tested specimens were reinforced by various reinforcement layouts. The behavior of tested beams was investigated. Observations were made on transverse displacement, primary cracking and ultimate failure load and distribution of strain on the face of tested panels. Based on those observations, the geometry of the concrete struts was examined. At least a new model to analysis of concrete struts was proposed based on modified compression field theory (MCFT). A database of 44 tested specimens was compiled to evaluate the proposed model. The results indicate that using the ACI and CSA expressions regarding the amount of minimum required reinforcement in a strut produces conservative but erratic results when compared with the test data. Conversely, the new proposed model presents a more accurate prediction for the strength of 44 tested struts.

In order to lighten the prestressed concrete solid members, nowadays, it is possible to make use of the advantage of HPC (fc>60 MPa) as well as replacing the solid section with a PSC thin-walled section for certain members such as circular and box columns. Using the strength theory of ACI, a numerical procedure along with a computer program was developed for the analysis of such sections subjected to axial compression or tension load and bending moments. The program solves for all possible variables such as, concrete compressive strength (fc= 60-100 MPa), type of prestressed steel, concrete cover, ratio of wall thickness to the section dimensions and the PS steel arrangements to satisfy the given loading cases, thus leading to an optimal cost solution. However, since the cross section is thin-walled circular or box and the PS steel is located at discrete points along the periphery of a circle or rectangle, the equations of equilibrium are complex for hand computations (especially for circular section) but suitable for computer program. So, by use of MATLAB software the interaction diagrams were also drawn for the analysis of such sections for all mentioned variables. The use of such diagrams is a safe and easy tool for the analysis of such columns. Finally the results are compared with the worked examples and a very good agreement is achieved.

The main objective of this study is to drive a simple solution for prediction of steel fiber reinforced concrete (SFRC) behavior under four point bending test (FPBT). In this study the concrete constitutive model has been supposed as a bilinear elastic-perfectly plastic stress-strain response in compression and a linear response up to tensile strength for tension. An exponential relation has been assumed for stress-crack opening in crack region. The assumed relation needs two parameters. The moment capacity is calculated by applying these assumptions and satisfying equilibrium law at critical cracked section. After that, parametric studies have been done on the behavior of SFRC. Finally the proposed model has been validated with some existing experimental test.

A comparison between design codes i.e. ACI and AISC-LRFD in evaluation of flexural strength of concrete filled steel tubular columns (CFTs) is examined. For this purpose an analytical study on the response of CFTs under axial-flexural loading is carried using three-dimensional finite elements with elasto-plastic model for concrete with cracking and crushing capability and elasto-plastic kinematic hardening model for steel. The accuracy of the model is verified against previous test results. The nonlinear modeling of CFT columns shows that the minimum thickness that recommended by ACI and AISC-LRFD to prevent local buckling before the steel shell yielding for CFT columns could be increased. The comparison of analytical results and codes indicates that the accuracy of ACI in estimation of lateral strength of CFT columns is more appropriate than AISC-LRFD. The ACI lateral strength of CFTs is located on upper bond of the AISC-LRFD’s provisions. AISC-LRFD estimates the lateral strength conservatively but ACI in some ranges such as in short columns or under high axial load levels computes lateral strength in non-conservative manner. Supplementary provisions for post local buckling strength of CFT columns should be incorporated in high seismic region. This effect would be pronounced for column with high aspect ratio and short columns.

The aim of current study is to investigate the effect of Carbon Fiber Reinforced Polymer (CFRP) composite fabric on the fatigue response of reinforced concrete beams. To predict and trace the failure occurrence and its growth, a small notch was induced at the middle span in bottom surface for all of RC specimens. At the certain points, strains in concrete and CFRP were measured in each cycle. The upper limit of applied load was considered at the level of design service load for bridges. In addition, strain measurements facilitated to the calculation of interfacial shear stresses between concrete substrate and the CFRP layer. The variation of such stresses through load cycles will be presented and discussed. Load–deflection curves, strain responses and propagation of tension cracks would provide an insight on the performance of the CFRP strengthened beams subjected to different cycles of fatigue loading.

Barrel vaults are attractive space structures that cover large area without intermediate supports. In this paper, the charged search system (CSS) optimization algorithm is employed for optimal design of barrel vaults. This method utilizes the governing laws of Coulomb and Gauss from electrostatics and the Newtonian law of mechanics. The results demonstrate the efficiency of the discrete CSS algorithm compared to other heuristic algorithms.

Chloride ion ingress in concrete is the main reason of concrete corrosion. In real world both uncertainty and stochasticity are main attributes of almost all measurements including in testing and modeling of chloride content profile in concrete. Regarding these facts new models should be able to represent at least some of the uncertainties in the predictions. In this paper after inspiration from classical physics related diffusion and random walk concept a stochastic partial differential equation (SPDE) of diffusion is introduced to show a more realistic modeling/calibration scheme for construction of stochastic chloride content profile in concrete. Diffusion SPDE provides a consistent quantitative way of relating uncertainty in inputs to uncertainty in outputs. Although it is possible to run sensitivity analysis to get some statistical results from deterministic models but the nature of diffusion is inherently stochastic. Brownian motion process (Wiener process) is used in SPDE to simulate the random nature of the diffusion in heterogeneous media or random fields like concrete. The proposed method can be used to calibrate/model the chloride ion profile in concrete by only some limited data for a given depth. Then the stochastic characters of chloride ion diffusion can be simulated by langevin equation. Results of the method are compared with data from some references and all show good agreements.

Learning rapidly and competently has become a pre-eminent strategy for improving organizational performance in the new knowledge era. Improving dynamic learning capability is an exclusive strategy for corporate success in construction industry. Thus engineering design firms should implement OL to accomplish a state of readiness for change and develop a competence to respond and identify future business potentials. This study aims to analyze the relationship between organizational learning (OL) and performance improvement (PI) in civil engineering design firms of Turkish construction industry. The empirical data was collected through a questionnaire survey conducted to engineering design firms registered to the Turkish Chamber of Civil Engineers. The hypothesized model relationships were tested using structural equation modeling (SEM). This study provides empirical evidence for the importance of the relationship between OL constructs and the learning outcome, PI. The results show that each of the variables has a different role and significant positive impact on the OL process and organizational PI. Knowledge and lessons learned from the past that belong to individuals are converted into organisational property, made accessible to the other members of the organisation. Thus an appropriate organisational design will enable an organisation to execute better, learn faster, and change more easily.This study is the first attempt made to develop and apply a measurement tool to assess OL in the civil engineering design sector of Turkish Construction Industry.

Runoff simulation is a vital issue in water resource planning and management, due to its determinative role in water resources state. Different models with various levels of accuracy and precision are developed for this purpose considering different prediction time scales. In this paper, two long term runoff simulation methods including IHACRES and ANN (Artificial Neural Network) models are employed in the south eastern part of Iran and the results are compared. These models have been utilized to simulate 5-month runoff in the wet period of December-April. In IHACRES application, first the rainfall is predicted and then transformed to runoff using climatic signals. For this purpose the daily precipitation is downscaled using two models called SDSM and LARS-WG. The best results of these models are selected as IHACRES model input to be used for simulating the corresponding runoff. In application of the ANN model, effective large scale signals on rainfall and runoff variations in the study region such as SLP, SST and SLP difference are considered as model inputs. The performances of the considered models in real time planning of water resources is evaluated through calculating the SWSI drought index and comparing it to the observed data. According to the obtained results, the simulated runoff using the IHACRES model are more likely to be observed values and they could be employed with more certainty.

The objective of this work is to perform a direct numerical simulation of turbulent channel flow where all essential scales of motion are resolved due to variable time-stepping algorithm in various time advancement method and different discritized form of convection term. A pseudo spectral method (Fourier series in stream-wise and span-wise directions and Chebychev polynomial expansion in normal direction) is employed for the spatial derivatives. The time advancement is carried out by different semi-implicit and splitting schemes. Also Alternating and Linearized form are added to four commonly used forms of the convective term, referred to as divergence, Convection, skew-symmetric, and rotational. Spectral method based on the primitive variable formulation is used in Cartesian coordinates with two periodic and one non-periodic boundary condition in three dimensional directions Ω=[0,4π]×[-1,1]×[0,2π]. The friction Reynolds number for channel flow is set to be Reτ=175 and the computational grids of 128×65×128 are used in the x, y and z directions, respectively. The comparison is made between turbulent quantities such as the turbulent statistics, wall shear velocity, standard deviation of u and total normalized energy of instantaneous velocities in different time-discretization methods and different forms of nonlinear term. The present results show that third-order time-discretizations forward Euler for explicit terms and backward Euler for implicit terms can minimize the computational cost of integration by maximizing the time step, while keeping the CFL number near a threshold in time-discretization schemes. Also, the de-aliased results of turbulence statistics do indicate that different expressions of nonlinear terms have minor discrepancy in pseudo spectral method. The results show that the most desirable approach is a combination of variable time stepping third order backward difference algorithm and rotational form, which provides reduced cost and further accuracy improvements.