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Using Base Isolators in Bridges to Reduce the Dynamic Forces of Piers and Abutments
, M.Sc. Thesis Sharif University of Technology ; Jahanshahi, Mohsen (Supervisor)
Abstract
In recent years, the application of base isolation as a seismic design strategy for reducing the effects of earthquake ground motion has become an advantageous method and much effort has been devoted to base isolation research and there has been a growing acceptance of this approach. In this research, the effect of using base isolators in reducing the dynamic forces of piers and abutments of bridges is studied. More specifically double-span bridges are the target of this research. After modeling a regular bridge in a typical analysis program, it is excited by different earthquake accelerograms and then the effect of using base isolators in dissipating the earthquake energy is investigated
Identification of Damage Type and Location in Reinforced Concrete Piers of Slab– Beam Bridges Using Numerical Methods
, M.Sc. Thesis Sharif University of Technology ; Ahmadizadeh, Mahdi (Supervisor)
Abstract
Bridges are among the crucial elements of transportation networks, and play an important role in facilitating emergency relief efforts following earthquakes. For this reason, it is emparative to monitor their damages to ensure about their performace in earthquakes. The structure of a bridge is divided into two parts, namely the superstructure and substructure. Due to the relatively high rigidity and strength of superstructures, most of structural damage is usually concentrated in substructures, which may ultimately affect the overall stability of the bridge. Therefore, assessing the level of damage in the substructure is of utmost concern. This research attempts to evaluate the damage in the...
Experimental and Numerical Investigation of the Flow Field around Complex Bridge Piers with and without the Scour Hole
, Ph.D. Dissertation Sharif University of Technology ; Ataie Ashtiani, Behzad (Supervisor)
Abstract
Local scour around bridge piers is one of the main causes of bridge failures Application of existing equations to complex flow patterns is problematic and often leads to questionable results in the field applications. A lack of understanding of the complex flow field and erosion mechanisms seems to be at least partly responsible for this state. Despite the rapid expansion of the literature on the flow around cylindrical piers, there are still challenges for flow field comprehension and estimating design scour depths around complex bridge piers. Due to geotechnical and economical reasons, bridge designs often leads to a complex foundation. Laboratory studies of local scour around complex...
Prediction of Scour Depth Around Complex Piers Using Classification Methods
, M.Sc. Thesis Sharif University of Technology ; Ataie-Ashtiani, Behzad (Supervisor) ; Jamali, Mirmosaddegh (Co-Advisor)
Abstract
In this study, existing prediction methods of maximum scour depth around complex piers are studies using available experimental data and a new relationship for scour prediction is presented. Complex pier consists of a column, pile cap and pile group and is frequently used for foundation of bridge piers in hydraulic and marine structures. The results of 52 clear-water scour experiments on 4 CP models are reported which can be valuable to hydraulic design of a CP. The 4 models had different values of pile cap thickness and number of piles inline with the flow and were tested at different pile cap elevations. The duration of experiments ranged from 24 to 120 hours. Then a database of laboratory...
Experimental investigation of clear-water local scour of compound piers
, Article Journal of Hydraulic Engineering ; Volume 136, Issue 6 , June , 2010 , Pages 343-351 ; 07339429 (ISSN) ; Baratian Ghorghi, Z ; Beheshti, A. A ; Sharif University of Technology
2010
Abstract
Local scour around complex piers under steady clear-water condition was studied experimentally for a variety of configuration, including different sizes and shapes of complex piers. A total of 70 experiments were carried out. Three sets of experiments were performed over the entire range of possible pile cap elevations for complex piers with different geometrical characteristics. The collected data are used to quantify the pile cap elevations that maximize or minimize the local scour depth. Some of the available methodologies to estimate the maximum local scour depth around such complex piers are evaluated. The predictions of the scour depths improved by using the revised methods of...
Neural network and neuro-fuzzy assessments for scour depth around bridge piers
, Article Engineering Applications of Artificial Intelligence ; Volume 20, Issue 3 , 2007 , Pages 401-414 ; 09521976 (ISSN) ; Borghei, S. M ; Jeng, D. S ; Sharif University of Technology
2007
Abstract
The mechanism of flow around a pier structure is so complicated that it is difficult to establish a general empirical model to provide accurate estimation for scour. Interestingly, each of the proposed empirical formula yields good results for a particular data set. Hence, in this study, alternative approaches, artificial neural networks (ANNs) and adaptive neuro-fuzzy inference system (ANFIS), are proposed to estimate the equilibrium and time-dependent scour depth with numerous reliable data base. Two ANN models, multi-layer perception using back-propagation algorithm (MLP/BP) and radial basis using orthogonal least-squares algorithm (RBF/OLS), were used. The equilibrium scour depth was...
Prediction of current-induced local scour around complex piers: Review, revisit, and integration
, Article Coastal Engineering ; Volume 133 , 2018 , Pages 43-58 ; 03783839 (ISSN) ; Ataie Ashtiani, B ; Beheshti, A ; Hadjzaman, M ; Jamali, M ; Sharif University of Technology
Elsevier B.V
2018
Abstract
Complex piers (CPs), consisting of a column, pile cap and pile group, are commonly built as foundations for hydraulic and marine structures. Scour-hole development around CPs is studied in this paper. A total of 52 tests is carried out on 4 CP models, with experiments durations ranging from 24 to 120 h. All of the available experimental data for clear-water scour around CPs including the collected data of the present study and those previously published are reviewed and combined into a database. A special case of bridge piers with deep foundation or caisson instead of pile caps is also considered, which is herein called compound piers. The database contains 367 experiments for CPs and 162...
Influence of unsteady flow hydrograph shape on local scouring around bridge pier
, Article Proceedings of the Institution of Civil Engineers: Water Management ; Volume 165, Issue 9 , October , 2012 , Pages 473-480 ; 17417589 (ISSN) ; Kabiri-Samani, A ; Banihashem, S. A ; Sharif University of Technology
ICE Pub
2012
Abstract
Accurate estimation of scour depth is needed for economic and safe determination of bridge pier foundation depth. Most design criteria are based on maximum scour depth due to the steady design discharge without flow time limit. In this paper, the results are presented of an experimental investigation on local scouring around a single bridge pier under steady and unsteady flow regimes. For unsteady flow, triangular shape hydrographs with repeatable peaks have been chosen. Results show that both sharp and flat increases to the peak of hydrographs have a negligible effect on scour depth for the same base time. An equation is obtained to compute the scour depth due to a specific triangular...
Local scour at open-channel junctions
, Article Journal of Hydraulic Research ; Volume 48, Issue 4 , Sep , 2010 , Pages 538-542 ; 00221686 (ISSN) ; Jabbari Sahebari, A ; Sharif University of Technology
2010
Abstract
High bed-shear stress resulting from secondary flows and velocity increase at a channel junction cause local erosion and deposition in natural rivers and earth-lined channels. Herein, the scour patterns at the junction of two loose bed channels were studied under clear-water conditions. The main dimensionless variables are the angle between the two approach flow branches, the discharge and width ratios of the tributary to the downstream channel branches, and the ratio of the mean downstream velocity to the threshold velocity. The results indicate that the position of the maximum scour depth temporally moves to the outer wall and upstream to the main channel, as affected by the dimensionless...
Scour hole influence on turbulent flow field around complex bridge piers
, Article Flow, Turbulence and Combustion ; Volume 97, Issue 2 , 2016 , Pages 451-474 ; 13866184 (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
Springer Netherlands
Abstract
Experimental results of detailed flow measurements using an Acoustic-Doppler Velocimeter (ADV) around a complex bridge pier (CBP) are presented. The pier consists of a column, a pile cap (PC) and a 2×4 pile group. The time-averaged velocities, turbulence intensities, and Reynolds stresses are studied and presented at different horizontal and vertical planes. Streamlines obtained from the velocity fields are used to show the complexity of the flow around the pier. It is shown that the main feature of the flow responsible for the entrainment of the bed sediments is a contracted (pressurized) flow below the PC toward the piles. A deflected flow around the PC and a strong down-flow along its...
Estimation of current-induced scour depth around pile groups using neural network and adaptive neuro-fuzzy inference system
, Article Applied Soft Computing Journal ; Volume 9, Issue 2 , 2009 , Pages 746-755 ; 15684946 (ISSN) ; Beheshti, A. A ; Ataie Ashtiani, B ; Sabbagh Yazdi, S. R ; Sharif University of Technology
2009
Abstract
The process of local scour around bridge piers is fundamentally complex due to the three-dimensional flow patterns interacting with bed materials. For geotechnical and economical reasons, multiple pile bridge piers have become more and more popular in bridge design. Although many studies have been carried out to develop relationships for the maximum scour depth at pile groups under clear-water scour condition, existing methods do not always produce reasonable results for scour predictions. It is partly due to the complexity of the phenomenon involved and partly because of limitations of the traditional analytical tool of statistical regression. This paper addresses the latter part and...
Experimental study of three-dimensional flow field around a complex bridge pier
, Article Journal of Engineering Mechanics ; Volume 136, Issue 2 , 2010 , Pages 143-154 ; 07339399 (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
2010
Abstract
In this paper, three-dimensional turbulent flow field around a complex bridge pier placed on a rough fixed bed is experimentally investigated. The complex pier foundation consists of a column, a pile cap, and a 2×4 pile group. All of the elements are exposed to the approaching flow. An acoustic-Doppler velocimeter was used to measure instantaneously the three components of the velocities at different horizontal and vertical planes. Profiles and contours of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses, as well as velocity vectors are presented and discussed at different vertical and horizontal planes. The approaching...