Contribution of gravity frames to seismic performance of steel moment resisting frames

Traditionally, lateral stiffness and strength of the gravity frames in steel buildings are neglected in structural analysis. During the past earthquakes, such as Northridge, USA, 1994 and Kobe, Japan, 1995, unexpected failures were detected at beam-to-column connections of steel moment resisting frames (MRFs). In the aftermath of these earthquakes, extensive research has been carried out to reveal the causes of these failures. Based on the detailed observations, it is likely that the reserve capacity provided by the gravity frames prevented the highly damaged steel buildings from collapsing, since majority of the moment-resisting connections failed prematurely during the Northridge earthquake (1994). Even though the influence of gravity frames (GFs) on structural behavior can be substantial, little attention is paid to evaluate its impact on structural response. With this paper, the contribution of interior GFs in seismic performance of special moment resisting steel frames (SMRFs) is evaluated. For this purpose, 4- and 9-story SMRFs were designed in accordance with the requirements of Draft Turkish Seismic Code (2016). The frames are, then, subjected to incremental dynamic analysis. To evaluate the contribution of the interior GFs on the overall seismic performance of structural system, inelastic behavior of shear tab (simple) connections at beam-to-gravity-only columns were idealized as semi-rigid joints. A general purpose structural analysis software, ETABS, is utilized for the analyses. The results of the study are presented in terms of story drifts, base shear vs. roof displacement

Seismic evaluation of square HSS braces in SCBF using regression analysis

Since the 1990s, structural engineering practice geared toward the use of hollow structural sections (HSS), notably square HSS, for their economy, and ease of design and construction. According to the AISC Seismic Provisions, during a severe earthquake, these braces could undergo post-buckling axial deformations 10 to 20 times their yielding deformation. However, recent experimental studies indicate that braces made of square HSS, depending on their size, width-to-thickness, and slenderness ratio, are vulnerable to fracture even prior to 10. Therefore, relying on past experimental studies comprised of a few square HSS specimens to develop seismic requirements for SCBF with square HSS could lead to underestimation of the seismic risk. This paper aims to evaluate the fracture risk of braces in existing SCBFs designed in accordance with AISC 341-05 and AISC 341-16 through incremental dynamic analyses (IDA) along with experimentally developed regression model that estimates fracture.Scopus - Affiliation ID: 6010507

Short term effects of prescribed fire on soil microbial biomass of black pine forests

In this study, we were examined of changes microbial carbon (MBC) and microbial Nitrogen (MBN) after one month controlled fire. The study area consist of sloping and flat areas, high and low intensity of burnt areas and control areas (unburned) including (flat low intensity: FLI, flat high intensity: FHI, smooth low intensity: SLI, smooth high intensity: SHI and 0-5 cm and 5-10 cm depth soil). In terms of microbial carbon on the upper soil in the flat high intensity and upper and lower soil in the smooth high intensity, there was a significant differences between burning and unburning area. Also, microbial carbon has been reduced approximately 50 % in the burning area. İn terms of microbial nitrogen has been found a significant reduction between upper and lower soil in the smooth low intensity area. However, we found a significant increase in the lower soil on smooth high intensity area. With regard to microbial carbon were found a significant differences between the intensity of the effect of low and high fire in burning areas. There were a significant relationship between microbial carbon and microbial nitrogen and also organic matter. Microbial carbon was also found a positive correlation with Ph (?<0,05). As a result, in the short term of fire reducing of microbial biomass on the top soil (0-5 cm). In addition, microbial nitrogen was increased and microbial carbon was reduced after fire. Additionaly, after fire microbial nitrogen was increasing in the lower soil and microbial biomass may decrease the usability of the organic karbon

Impact of introducing semi-rigid moment frames on seismic response of braced frames

Maximum seismic inelastic drift demand in a steel building with braced frames as primary seismic-force-resisting (SFR) system tends to concentrate in few stories without considering inherent participation of designed gravity-force-resisting (GFR) system in actual structural stiffness and strength. The influence of GFR system on stiffness and strength can be taken into account by considering the composite action in beam-to-column shear connections that exist in modern steel building construction to form actual semi-rigid moment-resisting frames. Therefore, modeling semi-rigid moment frames as an equivalent to the GFR system in braced frame buildings could be utilized as a representative to the strength provided by gravity frames. This paper presents a seismic evaluation of a six-story chevron braced frame, with and without semi-rigid moment frame. Four different cases are investigated under a set of ground motions and results are discussed in terms of story drift distribution along the height. The results pointed out that the current findings lay a foundation to conduct further investigation on the seismic performance of braced frames as designed SFR system together with GFR system.Scopus - Affiliation ID: 6010507

Forest fire influence on microbial biomass of forest soils: a review

Microbial biomass is one of the important companent of the C and N cycling in soil. It directly affects soil biological activity. Being a storage medium for C and N, microbial biomass, interacts many biotic and abiotic environmental factors. Forest fires affect soil microbial biomass as other soil properties do. In this study, a general evaluation was made on the effects of forest fire on soil microbial biomass. In general, the effect of forest fire on soil microbial biomass is negative. Both natural and prescribed fires affect soil microbial carbon but the magnitude of the effect is larger in natural fires. This effect could be negative or positive in short term, but in long term the effect is mainly negative. The fire effected upper soil is generally adversly affected while the deeper soil is affected positively. Fire effect on microbial biomass should be evaluated considering climate and the other ecosystem companents all together

Nonlinear behaviour of liquefied natural gas tanks with different seismic isolation systems

Ovaj rad pobliže određuje učinke različitih tipova izolacijskih sustava na ponašanje spremnika za ukapljeni prirodni plin (engl. liquefied natural gas - LNG) tijekom potresa. Provedene su nelinearne analize primjenom vremenskog zapisa neizoliranih i triju različitih izoliranih modela za prosječno ubrzanje sedam vrsta gibanja tala stupnjevanih kako bi se postigla određena moguća sigurna obustava rada postrojenja tijekom potresa. Program ANSYS Workbench primijenjen je za modeliranje tekućine ukapljenog plina, unutarnjeg čeličnog spremnika, vanjske stijenke, serklaže, krova, betonskih temelja i izolacije stražnje stijenke. Program LS-DYNA primijenjen je za nelinearne analize tekućine LNG-a, unutarnjeg čeličnog spremnika i betonskih temelja. Uspoređeni su rezultati ukupne poprečne potresne sile u podnožju, visine zapljuskivanja, naprezanja čeličnog spremnika i bočnog pomaka. Rezultati su pokazali da nema razlike između konvektivnih i impulsnih modova za izolirane spremnike LNG-a. Zaključeno je da se valno gibanje tekućine razlikuje od osciliranja konstrukcije, a razdoblja protupotresnih izolacija nisu utjecala na zapljuskivanje. U neizoliranom su sustavu vrijednosti naprezanja dosegle 400 MPa, dok su te vrijednosti u izoliranim spremnicima za LNG prosječno iznosile 350 MPa.This study determines the effects of different types of base isolator systems on the seismic performance of liquefied natural gas (LNG) storage tanks. Nonlinear time-history analyses of the non-isolated and three different isolated models were performed for the average acceleration of seven ground motions scaled to achieve a specified safe shutdown earthquake. The ANSYS Workbench program was used in the modelling studies of the LNG liquid, inner steel tank, outer shell, ring beam, roof and concrete foundation and side wall insulation. The LS-DYNA program was used for the nonlinear analyses of the LNG liquid, inner steel tank and concrete foundation. The results of the total base shear force, sloshing height, steel tank stresses and lateral deflection were compared. The results indicated that there was no difference between the convective and impulsive modes for the LNG tanks with isolators. It was concluded that the wave motion of the liquid was different from the oscillation of the structure and the earthquake isolation times did not affect the sloshing motion. In the non-isolated system, the stress reached 400 MPa, whereas it was 350 MPa on average in the LNG tanks with isolators

Seismic assessment of ductile concentrically braced frames with HSS bracings

A study on the seismic ductility demands on square HSS braces in special concentrically braced frames (SCBFs) is presented to address the seismic risk of braces in existing SCBF buildings designed according to both previous and current AISC Seismic Provisions. First, the paper discusses the development of ductility-based fragility curves by employing specimens with various width-to-thickness and slenderness ratios collected from 16 experimental programs from 1978 to today. Second, the constructed fragility curves are used to estimate the vulnerability of square HSS braces to the damage state of fracture using the brace ductility demand as engineering demand parameter. Then, the seismic risk of braces in terms of fatigue life is evaluated under 30 earthquake ground motions using a seven-story office building designed following requirements of previous and current design practice. The study concludes that braces in SCBF designed in compliance with the previous and current AISC Seismic Provisions are subject to a high probability of fracture under earthquake ground motions characterized by different intensity levels, which in turn might lead to underestimation of the overall seismic risk.WOS:000471083200028Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ1ArticleUluslararası işbirliği ile yapılan - EVETTemmuz2019YÖK - 2018-1

Neural network based instant parameter prediction for wireless sensor network optimization models

Optimal operation configuration of a Wireless Sensor Network (WSN) can be determined by utilizing exact mathematical programming techniques such as Mixed Integer Programming (MIP). However, computational complexities of such techniques are high. As a remedy, learning algorithms such as Neural Networks (NNs) can be utilized to predict the WSN settings with high accuracy with much lower computational cost than the MIP solutions. We focus on predicting network lifetime, transmission power level, and internode distance which are interrelated WSN parameters and are vital for optimal WSN operation. To facilitate an efficient solution for predicting these parameters without explicit optimizations, we built NN based models employing data obtained from an MIP model. The NN based scalable prediction model yields a maximum of 3% error for lifetime, 6% for transmission power level error, and internode distances within an accuracy of 3m in prediction outcomes