Bulent Akbas

Seismic vulnerability mitigation of liquefied gas tanks using concave sliding bearings

The aim of this paper is to evaluate the effectiveness of a concave sliding bearing system for the seismic protection of liquefied gas storage tanks through a seismic fragility analysis. An emblematic case study of elevated steel storage tanks, which collapsed during the 1999 İzmit earthquake at Habas Pharmaceutics plant in Turkey, is studied. Firstly, a fragility analysis is conducted for the examined tank based on a lumped-mass stick model, where the nonlinear shear behaviour of support columns is taken into account by using a phenomenological model. Fragility curves in terms of an efficient intensity measure for different failure modes of structural components demonstrate the inevitable collapse of the tank mainly due to insufficient shear strength of the support columns. A seismic isolation system based on concave sliding bearings, which has been demonstrated a superior solution to seismically protect elevated tanks, is then designed and introduced into the numerical model, accounting for its non-linear behaviour. Finally, a vulnerability analysis for the isolated tank is performed, which proves a high effectiveness of the isolation system in reducing the probability of failure within an expected range of earthquake intensity levels.

Prediction of lateral confinement coefficient in reinforced concrete columns using neural network simulation

This paper presents an application of Neural Network (NN) simulation in civil engineering science. The confinement degree for confined concrete has been investigated by using a NN analysis as an alternative approach. To accurately predict the behavior of a confined concrete, it is important to understand the confinement degree and its individual components. For the purpose of investigating confinement effects, three empirical equations as a function of various parameters and an experimental work existing in the literature were considered in this study. However, these analytical models are time consuming to use. Therefore, there is still the need to develop simple but accurate method for determining the confinement coefficient. In this context, the NN algorithm has been established, in order to validate these empirical equations proposed for the confinement coefficient. The approach adapted in this study was shown to be capable of providing accurate estimates of lateral confinement coefficient, Ks by using the six design parameters. Finally, comparison with other empirical equations proposed for the lateral confinement coefficient illustrates the validity of the proposed algorithm.

Estimation of seismic-induced demands on column splices with a neural network model

The current seismic design specification (AISC 341-05) requires that column splices in moment frames, when not made using complete joint penetration (CJP) welds, be designed to develop the flexural strength of the smaller connected column and the shear demand associated with flexural hinging at the top and bottom of a spliced column at a given story. AISC 341-05 assumes that the beam-to-column connection would reach its critical limit state before the column splice does. Estimating seismic demands on column splices involves both ground motion and structural parameters, i.e., it is a high order nonlinear and complex problem. This study presents a Neural Network (NN) model to estimate the seismic demands on column splices in low-, medium-, and high-rise steel moment frames. Nine input parameters and 6 output parameters were used to construct the NN model. The effect of each input parameter on the output parameters (seismic demands on column splices and frame) was investigated through a sensitivity analysis based on the NN model.

Seismic Evaluation of Existing Wharf Structures Subjected to Earthquake Excitation: Case Study

The ability of aging shore structures to resist design seismic forces located in high-seismicity regions has been a subject of interest for many researchers. Seismic design codes have become more stringent and suggest the use of new design methods, such as performance-based design. According to the Turkish Code for Shore Structures (TCSS 2008), a pile-wharf structure is expected to withstand a D1 level of ground motion (corresponding to a return period of 72 years) with minor or no damage and a D2 level of ground motion (corresponding to a return period of 475 years) with short-term loss of serviceability. In this study, nonlinear static analyses of the seismic performance of two existing pile-wharf structures were performed (pushover analyses) according to TCSS (2008). The results are presented here.

Performance-Based Design of Buried Steel Pipes at Fault Crossings

Buried steel pipes are commonly used in oil and gas industry for transmitting hydrocarbon products. Fault crossing is considered as one of the most important extreme events. Buried steel pipes are more vulnerable to compressive strains as compared to tensile strains. Therefore, the orientation angle of the pipe with respect to the fault should be arranged in such a way so as to promote net tension in the pipe.In this study, a numerical study is carried out on a simplified numerical model to determine the seismic demand on steel pipes at fault crossings. The proposed model permits plastic hinge formation in the pipe due to incrementally applied fault movements, allow determining the critical length of the pipeline and measure strains developed on the tension and compression sides in the pipe. Based on the analyses carried out on the simple model and previous studies, two performance levels are defined for pipelines; namely, fully functional and partially functional.Copyright

Strain-Based Seismic Performance Evaluation of Prefabricated Structures

Precast concrete frame systems are widely preferred for the single storey industrial buildings in Turkey and Europe due to its rapid and economical construction practice. Field investigations after past major earthquakes revealed that the damage in such structures was primarily due to the improper detailing in beam–column connections and lack of required lateral stiffness. In this study, two different precast industrial buildings, damaged during the 1999 Marmara earthquake, were numerically investigated. The seismic performances of the buildings were evaluated by using Incremental Equivalent Seismic Load Method and strain-based damage definitions as recommended in Turkish Earthquake Code. The analytical results obtained from performance evaluations are compared with the findings from the field investigations.

Performance-Based Evaluation of Hydrocarbon Steel Pipes Under Internal Pressure

Hydrocarbon steel pipes have undertaken a very important and fundamental role in the oil and gas industries in the world. Although these pipes are simple structural forms, their structural behaviors are very complex and challenging for the structural engineering community. One of the fundamental problems for pipelines is plastic deformations under internal pressure. This study focuses on to develop a methodology for the performance evaluation of hydrocarbon steel pipes under internal pressure. In this perspective, a hydrocarbon pipe, which is used in natural gas pipelines, is modeled by nonlinear finite element model (FEM) and investigated in terms of structural behavior under different internal pressure conditions; operating pressure (100 bar), design pressure (150 bar) and high pressure (250 bar). In order to obtain an accurate solution, the finite element model is calibrated with a hydrostatic test, which is conducted on a pipe under 133 bar.

Seismic Performance and Retrofit Evaluation of an Existing Pile-Wharf Structure

AbstractPile-wharf structures are one of the substantial facilities for marine transportation along the shorelines. Due to their logistical significance, keeping the pile-wharf structures operation...

Designs of Special Concentrically Braced Frame Using AISC 341-05 and AISC 341-10

AbstractSpecial concentrically braced frames (SCBFs) are among the most common steel structures for resisting earthquake loads in high seismic regions. Concentrically braced frames (CBFs) are elastically designed as one vertical truss system to resist lateral loads through axial brace members when they are introduced. The explicit capacity-design approach has been fully incorporated into the newest seismic provisions for structural steel buildings. One new analysis section is added into AISC 341-10 to address the inelastic responses of SCBFs. Two separate structural analyses and one additional analysis are required for SCBFs in AISC 341-10. These analysis requirements significantly increase design efforts in typical design offices, and a comprehensive study to demonstrate how such an explicit inelastic design procedure would (or would not) significantly improve seismic performance of SCBFs appears to be justified. This paper summarizes the seismic design of three SCBFs with different heights, namely, 4, 1...

Seismic Energy Demands in Steel Moment Frames

This study presents an energy approach to the seismic evaluation of steel moment resisting frames. A structure subjected to strong ground motion is supposed that it shows nonlinear behavior. Energy parameters is a way to specify the structural damage. Input energy is depend on the characteristics of the structure and ground motion. Structural design can be defined as the equilibration of the input energy and the energy dissipation capacity of the structure. Structures subjected to eartquake are supposed to dissipate all the input energy. Studies based on energy concepts are usually applied to single-degree-of-freedom (SDOF) system. For multi-degree-of-freedom (MDOF), more researches and new simpler methodologies are still needed in performance based evaluation including energy parameters. In this study , low – medium and high rise steel moment frames and will be studied in linear and nonlinear time history analysis. The results obtained from these analysis are reviewed for seismic energy demands.