Failure analysis of steel column-RC base connections under lateral cyclic loading

Serhat Demir,Metin Husem,Selim Pul 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.50 No.4

One of the most important structural components of steel structures is the column-base connections which are obliged to transfer horizontal and vertical loads safely to the reinforced concrete (RC) or concrete base. The column-base connections of steel or composite steel structures can be organized both moment resistant and non-moment resistant leading to different connection styles. Some of these connection styles are ordinary bolded systems, socket systems and embedded systems. The structures are frequently exposed to cycling lateral loading effects causing fatal damages on connections like columns-to-beams or columns-to-base. In this paper, connection of steel column with RC base was investigated analytically andexperimentally. In the experiments, bolded connections, socket and embedded connection systems are taken into consideration by applying cyclic lateral loads. Performance curves for each connection were obtained according to experimental and analytical studies conducted and inelastic behavior of connections was evaluated accordingly. The cyclic lateral performance of the connection style of embedding the steel column into the reinforced concrete base and strengthening of steel column in upper level of base connection wasfound to be higher and effective than other connection systems. Also, all relevant test results were discussed.

Failure analysis of steel column-RC base connections under lateral cyclic loading

Demir, Serhat,Husem, Metin,Pul, Selim Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.50 No.4

One of the most important structural components of steel structures is the column-base connections which are obliged to transfer horizontal and vertical loads safely to the reinforced concrete (RC) or concrete base. The column-base connections of steel or composite steel structures can be organized both moment resistant and non-moment resistant leading to different connection styles. Some of these connection styles are ordinary bolded systems, socket systems and embedded systems. The structures are frequently exposed to cycling lateral loading effects causing fatal damages on connections like columns-to-beams or columns-to-base. In this paper, connection of steel column with RC base was investigated analytically and experimentally. In the experiments, bolded connections, socket and embedded connection systems are taken into consideration by applying cyclic lateral loads. Performance curves for each connection were obtained according to experimental and analytical studies conducted and inelastic behavior of connections was evaluated accordingly. The cyclic lateral performance of the connection style of embedding the steel column into the reinforced concrete base and strengthening of steel column in upper level of base connection was found to be higher and effective than other connection systems. Also, all relevant test results were discussed.

Investigation of bond-slip modeling methods used in FE analysis of RC members

Serhat Demir,Metin Husem 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.56 No.2

Adherence between reinforcement and the surrounding concrete is usually ignored in finite element analysis (FEA) of reinforced concrete (RC) members. However, load transition between the reinforcement and surrounding concrete effects RC members’ behavior a great deal. In this study, the effects of bond-slip on the FEA of RC members are examined. In the analyses, three types of bond-slip modeling methods (perfect bond, contact elements and spring elements) and three types of reinforcement modeling methods (smeared, one dimensional line and three dimensional solid elements) were used. Bond-slip behavior between the reinforcement and surrounding concrete was simulated with cohesive zone materials (CZM) for the first time. The bond-slip relationship was identified experimentally using a beam bending test as suggested by RILEM. The results obtained from FEA were compared with the results of four RC beams that were tested experimentally. Results showed that, in FE analyses, because of the perfect bond occurrence between the reinforcement and surrounding concrete, unrealistic strains occurred in the longitudinal reinforcement. This situation greatly affected the load deflection relationship because the longitudinal reinforcements dominated the failure mode. In addition to the spring elements, the combination of a bonded contact option with CZM also gave closer results to the experimental models. However, modeling of the bond-slip relationship with a contact element was quite difficult and time consuming. Therefore bond-slip modeling is more suitable with spring elements.

The cyclic behavior of steel polyoxymethylene composite braces

Serhat Demir 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.70 No.5

Steel tubular buckling controlled braces are well known as being simple, practical and cost-effective lateral force resisting systems. Although these system features have gained the attention of the researchers over the last decade, steel tubular buckling controlled braces currently have limited application. Indeed, only a few steel tubes tightly encased within each other exist in the steel industry. In this paper, a new and practical design method is proposed in order to better promote the widespeared application for current steel tubular buckling controlled brace applications. In order to reach this goal, a holed-adapter made with polyoxymethylene adaptable to all round and square steel sections, was developed to use as infiller. The research program presents designing, producing and displacement controlled cyclic loading tests of a conventional tubular brace and a buckling controlled composite brace. In addition, numerical analysis was carried out to compare the experimental results. As a result of the experimental studies, buckling was controlled up to 0.88 % drift ratio and the energy dissipation capacity of the conventional tubular brace increased 1.46 times due to the proposed design. The main conclusion of this research is that polyoxymethylene is a highly suitable material for the production of steel tubular buckling controlled braces.

Utilization Potential of Fly Ash together with Silica Fume in Autoclaved Aerated Concrete Production

M. Serhat Baspinar,Ismail Demir,Erhan Kahraman,Gokhan Gorhan 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.1

The increase in the number of thermal power plants has led to the production of an increasing amount of fly ash that causes high environmental impact in Turkey. Many researchers around the world are looking at methods of gainful utilization and disposal of fly ash. However, the construction materials industry is the most suitable way to mass consumption of the fly ash waste. In this study, the utilization potential of fly ash and silica fume in Autoclaved Aerated Concrete (AAC) production were investigated. Optimum fly ash/cement ratio was determined, and this composition was improved by the silica fume addition. Strength-Microstructure relations of the products were investigated. Crystalline C-S-H phases of Tobermorite and Xonotlite were developed after autoclaving at 4 bar. Silica fume addition was found to be useful for the prevention of the ettringite phase in the product. Silica fume addition improved the hydrothermal conditions during the autoclaving of the mixtures.

Experimental investigation of a prefabricated timber-concrete composite floor structure: Notched-slab approach

Yilmaz, Semih,Demir, Serhat,Vural, Nilhan Techno-Press 2021 Advances in concrete construction Vol.12 No.1

This study presents the experimental performance of a high ductility and energy dissipation capacity connector named notched-slab fastener, which is developed for timber-concrete composite floor structures. Notched-slab fastener is unique because the notch was left in the concrete slab instead of a timber beam for the first time. In this way, cross-section loss in the timber beam is prevented. This is one of the most important benefits of the proposed connector. Experimental performance of the purposed connector was investigated with two test methods: push-out test and bending test. For comparison purposes, a notched fastener was also produced and tested as reference sample. Test results showed that notched-slab fastener has stable load carrying behavior under push-out loading with high-energy dissipation and no sudden strength degradation. In addition, notched slab design provided moment arm to the fastener and the damage is concentrated in the connector instead of concrete.

Diagonal bracing of steel frames with multi-cable arrangements

Metin Husem,Serhat Demir,Hong G. Park,Suleyman I. Cosgun 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.59 No.6

A large number of structure in the world were build with poor seismic details, with or without any lateral load resisting system like concentrically braced frames and steel plate shear walls. These structures can reveal deteriorating hysteretic behaviors with stiffness and strength degradation. Therefore, seismic retrofitting of such structures for drift control has vital importance. In this study a retrofit methodology has been developed, which involves diagonal bracing of steel frames with different cable arrangements. In the experimental and numerical program 5 different lateral load resisting system were tested and results compared with each other. The results indicated that multi-cable arrangements suggested in this study showed stable ductile behavior without any sudden decrease in strength. Due to the usage of more than one diagonal cable, fracture of any cable did not significantly affect the overall strength and deformation capacity of the system. In cable braced systems damages concentrated in the boundary zones of the cables and beams. That is why boundary zone must have enough stiffness and strength to resist tension field action of cables.

Experimental and numerical analyses on determination of indirect (splitting) tensile strength of cemented paste backfill materials under different loading apparatus

Komurlu, Eren,Kesimal, Ayhan,Demir, Serhat Techno-Press 2016 Geomechanics & engineering Vol.10 No.6

The indirect tensile strengths (ITSs) of different cemented paste backfill mixes with different curing times were determined by considering crack initiation and fracture toughness concepts under different loading conditions of steel loading arcs with various contact angles, flat platens and the standard Brazilian test jaw. Because contact area of the ITS test discs developes rapidly and varies in accordance with the deformability, ITSs of curing materials were not found convenient to determine under the loading apparatus with indefinite contact angle. ITS values increasing with an increase in contact angle can be measured to be excessively high because of the high contact angles resulted from the deformable characteristics of the soft paste backfill materials. As a result of the change of deformation characteristics with the change of curing time, discs have different contact conditions causing an important disadvantage to reflect the strength change due to the curing reactions. In addition to the experimental study, finite element analyses were performed on several types of disc models under various loading conditions. As a result, a comparison between all loading conditions was made to determine the best ITSs of the cemented paste backfill materials. Both experimental and numerical analyses concluded that loading arcs with definite contact angles gives better results than those obtained with the other loading apparatus without a definite contact angle. Loading arcs with the contact angle of $15^{\circ}$ was found the most convenient loading apparatus for the typical cemented paste backfill materials, although it should be used carefully considering the failure cracks for a valid test.

Periodontal Status of Chronic Renal Failure Patients Receiving Hemodialysis

Ismail Marakoglu,Ulvi Kahraman Gursoy,Serhat Demirer,Hafize Sezer 연세대학교의과대학 2003 Yonsei medical journal Vol.44 No.4

Host factors such as systemic diseases, genetic polymorphism or drug usage play a major role in the pathogenesis of periodontal disease by modifying the host response to periodontal infection or altering the susceptibility to infection by periodontal organisms. This study was designed to evaluate the clinical response of patients receiving hemodialysis to existing microbial dental plaque. Gingival Index (GI) and Plaque Index (PI) scores and probing depths (PD) were recorded for the entire dentition on 36 chronic renal failure patients receiving hemodialysis (H) and 36 systemically healthy individuals (C), matched with the patient group, based on age and extent of plaque accumulation. No statistically significant difference was observed in the clinical parameters between the two groups (PI: t=1.69 p= 0.096; GI: t=1.057 p=0.294; PD: t=0.01 p=0.99). In the present study, H patients revealed a similar response to existing bacterial plaque and their periodontal status was comparable to that of the control group. Although patients receiving hemodialysis have been suggested to present a certain degree of immunosuppression, based on the findings of the present study chronic renal failure does not seem to be an additional risk factor for more severe periodontal destruction. Host factors such as systemic diseases, genetic polymorphism or drug usage play a major role in the pathogenesis of periodontal disease by modifying the host response to periodontal infection or altering the susceptibility to infection by periodontal organisms. This study was designed to evaluate the clinical response of patients receiving hemodialysis to existing microbial dental plaque. Gingival Index (GI) and Plaque Index (PI) scores and probing depths (PD) were recorded for the entire dentition on 36 chronic renal failure patients receiving hemodialysis (H) and 36 systemically healthy individuals (C), matched with the patient group, based on age and extent of plaque accumulation. No statistically significant difference was observed in the clinical parameters between the two groups (PI: t=1.69 p= 0.096; GI: t=1.057 p=0.294; PD: t=0.01 p=0.99). In the present study, H patients revealed a similar response to existing bacterial plaque and their periodontal status was comparable to that of the control group. Although patients receiving hemodialysis have been suggested to present a certain degree of immunosuppression, based on the findings of the present study chronic renal failure does not seem to be an additional risk factor for more severe periodontal destruction.

A new type notched slab approach for timber-concrete composite construction: Experimental and numerical investigation

Semih Yılmaz,Olguhan Şevket Karahasan,Ahmet Can Altunışık,Nilhan Vural,Serhat Demir 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.81 No.6

Timber-Concrete Composite construction system consists of combining timber beam or deck and concrete with different connectors. Different fastener types are used in Timber-Concrete Composite systems. In this paper, the effects of two types of fasteners on structural behavior are compared. First, the notches were opened on timber beam, and combined with reinforced concrete slab by fasteners. This system is called as Notched Connection System. Then, timber beam and reinforced concrete slab were combined by new type designed fasteners in another model. This system is called as Notched-Slab Approach. Two laboratory models were constructed and bending tests were performed to examine the fasteners' effectiveness. Bending test results have shown that heavy damage to concrete slab occurs in Notched Connection System applications and the system becomes unusable. However, in Notched-Slab Approach applications, the damage concentrated on the fastener in the metal notch created in the slab, and no damage occurred in the concrete slab. In addition, non-destructive experimental measurements were conducted to determine the dynamic characteristics. To validate the experimental results, initial finite element models of both systems were constituted in ANSYS software using orthotropic material properties, and numerical dynamic characteristics were calculated. Finite element models of Timber-Concrete Composite systems are updated to minimize the differences by manual model updating procedure using some uncertain parameters such as material properties and boundary conditions.