Civil Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10679/312

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Now showing 1 - 7 of 7

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Analysis of offshore wind turbine by considering soil-pile-structure interaction: effects of foundation and sea-wave properties
(Taylor & Francis, 2022) Fard, Maryam Massah; Erken, A.; Erkmen, Bülent; Ansal, Mustafa Atilla; Civil Engineering; FARD, Maryam Massah; ERKMEN, Bülent; ANSAL, Mustafa Atilla
Prediction of the dynamic performance of an offshore wind turbine (OWT) requires consideration of many different design parameters. Besides the superstructure, the OWT foundation also plays an important role both functionally and financially in the design. In this study, numerical dynamic analyses of an offshore wind turbine with a monopile foundation are performed under wave loading that may lead to soil liquefaction around the pile due to cyclic stresses induced by the pile displacements using the open-source program, OpenSees. Effects of foundation properties such as monopile diameter, pile embedment depth, and sea-wave characteristics such as its period, sea-water depth, duration, and level of the loading on the dynamic performance of the system are investigated. The results in terms of deformations, excess pore water pressure, and inertial forces are presented and discussed. The findings are considered as valuable guidance on the estimation of the dynamic performance and liquefaction susceptibility of the offshore wind turbine foundations under cyclic sea-wave loads.
Open Access
Comparison of blast analysis methods for modular steel structures
(Turkish Chamber of Civil Engineers, 2018-03) Erkmen, Bülent; Civil Engineering; ERKMEN, Bülent
Two blast analysis methods widely used are three-dimensional finite element (FE) and uncoupled equivalent single degree of freedom (ESDOF) methods. The uncoupled equivalent ESDOF method, which is the most common blast analysis method, provides considerable advantages and simplicity in analysis and design stages. However, the inherent assumptions and simplifications involved but especially neglecting member's dynamic interactions can significantly affect accuracy of analysis results. In this study, blast performance of a prototype two-module steel blast-resistant building is evaluated using uncoupled ESDOF and FE methods. The results are compared to evaluate adequacy of uncoupled ESDOF method for blast analysis of the structure.
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A computational workflow for rupture‐to‐structural‐response simulation and its application to Istanbul
(Wiley, 2020-10) Zhang, W. Y.; Restrepo, D.; Crempien, J. G. F.; Erkmen, Bülent; Taborda, R.; Kurtuluş, Aslı; Taciroglu, E.; Civil Engineering; ERKMEN, Bülent; KURTULUŞ, Asli
Scenario-based earthquake simulations at regional scales hold the promise in advancing the state-of-the-art in seismic risk assessment studies. In this study, a computational workflow is presented that combines (i) a broadband Green's function-based fault-rupture and ground motion simulation-herein carried out using the "UCSB (University of California at Santa Barbara) method", (ii) a three-dimensional physics-based regional-scale wave propagation simulation that is resolved at fmax=11.2 Hz, and (iii) a local soil-foundation-structure finite element analysis model. These models are interfaced with each other using the domain reduction method. The innermost local model-implemented in ABAQUS-is additionally enveloped with perfectly matched layer boundaries that absorb outbound waves scattered by the structures contained within it. The intermediate wave propagation simulation is carried out using Hercules, which is an explicit time-stepping finite element code that is developed and licensed by the CMU-QUAKE group. The devised workflow is applied to a 80x40x40 km3 region on the European side of Istanbul, which was modeled using detailed soil stratigraphy data and realistic fault rupture properties, which are available from prior microzonation surveys and earthquake scenario studies. The innermost local model comprises a chevron-braced steel frame building supported by a shallow foundation slab, which, in turn, rests atop a three-dimensional soil domain. To demonstrate the utility of the workflow, results obtained using various simplified soil-structure interaction analysis techniques are compared with those from the detailed direct model. While the aforementioned demonstration has a limited scope, the devised workflow can be used in a multitude of ways, for example, to examine the effects of shallow-layer soil nonlinearities and surface topography, to devise site- and structure-specific seismic fragilities, and for calibrating regional loss models, to name a few.
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Effects of unbonded steel layout on seismic behavior of post-tensioned precast concrete shear walls
(Springer Nature, 2020-10) Erkmen, Bülent; Civil Engineering; ERKMEN, Bülent
Unbonded post-tensioned precast connections have been studied widely in various applications and shown to be promising seismic resisting systems with superior seismic performance including exceptional self-centering capability and minimized structural damage. In this paper, effects of unbonded post-tensioned steel layout of precast concrete shear walls on seismic performance of a typical five-story precast concrete parking garage structure with the walls being the only lateral load resisting system is studied. The seismic behavior of the walls is determined using static nonlinear push-over, cyclic, and nonlinear time-history dynamic analyses under both the design and survival level ground motions. Three prototype unbonded post-tensioned precast concrete shear walls are designed with different unbonded post-tensioning steel tendon layout. Roof drift, post-tensioning force, and base shear and normal forces at the wall-foundation horizontal joint are monitored, and the demand for the coefficient of shear friction along the horizontal joint is calculated. The results show that seismic behavior of unbonded post-tensioned precast shear walls, in particular, maximum building drift, permanent losses in post-tensioning steel force, and coefficient of shear friction, is significantly influenced by layout of unbonded post-tensioned steel. The results and findings presented are valuable to improve design guidelines and provide a useful reference for practical applications of unbonded post-tensioned precast concrete connections in seismic applications.
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Evaluation of code provisions for seismic performance of unachored liquid storage tanks
(2017) Erkmen, Bülent; Civil Engineering; ERKMEN, Bülent
Seismic performance of two unanchored liquid-storage tanks with tank diameter of 24.5 m and 36 m and operating liquid height of 12.2 m and 20.0 m, respectively were investigated using Coupled Eulerian-Lagrangian (CEL) and mechanical spring-mass analogy nonlinear finite element computational methods. The CEL approach includes the effects of higher modes of liquid vibration (sloshing), liquid breaking effects, and liquid-structure interaction during seismic loading. The modern seismic design provisions for liquid-storage tanks, on the other hand, are based on a mechanical spring-mass analogy. This approach neglects the higher vibration modes for the sloshing water, liquid-structure interaction, and effects of tank base uplift on seismic performance. For the tanks, base uplift histories were computed with both modeling approaches through nonlinear time history analysis performed using five recorded earthquake acceleration data. The uplift histories were compared to evaluate the adequacy of code seismic design provisions for unanchored tanks, and to determine whether the mechanical spring-mass analogy can be used to predict seismic performance of unanchored tanks. Analysis results show that the traditional mechanical spring-mass analogy, which is the basis for the current seismic design provisions, does not capture tank uplift history and its effects on dynamic loads. This approach underpredicts the total numbers of tank uplifts during seismic loading. The maximum tank base uplift computed using mechanical spring-mass analogy had an average error between 22% and 58 % for each tank. The results show that there is a need to developed a modify version of the traditional mechanical spring-mass analogy to be used for predicting seismic performance of unanchored liquid-storage tanks.
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Numerical modeling of the offshore wind turbine monopile foundation under environmental loading
(CRC Press, 2019) Fard, Maryam Massah; Erken, A.; Erkmen, Bülent; Ansal, Mustafa Atilla; Civil Engineering; Silvestri, F.; Moraci, N.; FARD, Maryam Massah; ERKMEN, Bülent; ANSAL, Mustafa Atilla
Prediction of dynamic performance of an offshore wind turbine requires consideration of many different design parameters. Beside the superstructure, foundation also plays an important role both functionally and financially in their design. In this study, numerical dynamic analysis of an offshore wind turbine with a monopile foundation is performed under wave action that may lead to liquefaction around pile diameter due to the cyclic stresses induced by the pile displacements. The effects of foundation characteristic such as monopile diameter and its embedment depth are investigated. The results in terms of displacements, excess pore water pressure, and inertial forces are presented and discussed. Findings are considered to give better estimation of the dynamic performance and liquefaction susceptibility of the offshore wind turbines foundations under cyclic loads induced by the pile displacements.
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Relationship between response modification coefficient and displacement amplification factor for different seismic levels and site classes
(National Technical University of Athens, 2019) Erkmen, Bülent; Civil Engineering; Papadrakakis, M.; Fragiadakis, M.; ERKMEN, Bülent
Modern seismic design provisions allow structural systems to be designed for reduced forces, which are typically much smaller than the corresponding elastic design loads. This reduction in seismic loads is done by using response modification coefficient. The maximum deflection or drift of structural systems is typically predicted by scaling deflections corresponding to this reduced force on elastic line by displacement amplification factor. The values of these two seismic design factors, which are independent of seismic level and site (soil) class for a given type of structure, are mostly based on accumulated experience from past earthquakes and engineering judgment. In this study, a large number of five story parking garage structures were designed with a range of response modification factors for two seismic levels and for different site classes. The seismic performance of the structures was determined by performing nonlinear time history analysis with several recorded earthquake records on corresponding site classes. The computed maximum drift values were used to develop relationship between response modification coefficient and corresponding deflection amplification factor for each site class and seismic level. The results show that these two seismic design parameters are related but seismic level and site classes does not have significant effects on the relationship.

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