Fire Resistance Studies on High Strength Steel Structures

Wang, Wei-Yong,Xia, Yue,Li, Guo-Qiang Council on Tall Building and Urban Habitat Korea 2018 International journal of high-rise buildings Vol.7 No.4

High strength steels have been widely applied in recent years due to high strength and good working performance. When subjected to fire conditions, the strength and elastic modulus of high strength steels deteriorate significantly and hence the load bearing capacity of structures reduces at elevated temperatures. The reduction factors of mechanical properties of high strength steels are quite different from mild steels. Therefore, the fire design methods deduced from mild steel structures are not applicable to high strength steel structures. In recent ten years, the first author of this paper has carried out a lot of fundamental research on fire behavior of high strength steels and structures. Summary of these research is presented in this paper, including mechanical properties of high strength steels at elevated temperature and after fire exposure, creep response of high strength steels at elevated temperature, residual stresses of welded high strength steel member after fire exposure, fire resistance of high strength steel columns, fire resistance of high strength steel beams, local buckling of high strength steel members, and residual strength of high strength steel columns after fire exposure. The results show that the mechanical properties of high strength steel in fire condition and the corresponding fire resistance of high strength steel structures are different from those of mild steel and structures, and the fire design methods recommended in current design codes are not applicable to high strength steel structures.

Moment redistribution of continuous composite I-girder with high strength steel

Joo, Hyun Sung,Moon, Jiho,Sung, Ik-Hyun,Lee, Hak-Eun 테크노프레스 2015 Steel and Composite Structures, An International J Vol.18 No.4

The continuous composite I-girder should have a sufficient rotation capacity (or ductility) to redistribute the negative bending moment into an adjacent positive bending moment region. However, it is generally known that the ductility of the high strength steel is smaller than that of conventional steel, and application of high strength steel can cause ductility problems in a negative moment region of the I-girder. In this study, moment redistribution of the continuous composite I-girder with high strength steel was studied, where high strength steel with yield stress of 690 MPa was considered (the ultimate stress of the steel was 800 MPa). The available and required rotation capacity of the continuous composite I-girder with high strength steel was firstly derived based on the stress-strain curve of high strength steel and plastic analysis, respectively. A large scale test and a series of non-linear finite element analysis for the continuous composite I-girder with high strength steel were then conducted to examine the effectiveness of proposed models and to investigate the effect of high strength steel on the inelastic behavior of the negative bending moment region of the continuous composite I-girder with high strength steel. Finally, it can be found that the proposed equations provided good estimation of the requited and available rotation capacity of the continuous composite I-girder with high strength steel.

Moment redistribution of continuous composite I-girder with high strength steel

주현성,이학은,문지호,성익현 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.4

The continuous composite I-girder should have a sufficient rotation capacity (or ductility) to redistribute the negative bending moment into an adjacent positive bending moment region. However, it is generally known that the ductility of the high strength steel is smaller than that of conventional steel, and application of high strength steel can cause ductility problems in a negative moment region of the I-girder. In this study, moment redistribution of the continuous composite I-girder with high strength steel was studied, where high strength steel with yield stress of 690 MPa was considered (the ultimate stress of the steel was 800 MPa). The available and required rotation capacity of the continuous composite I-girder with high strength steel was firstly derived based on the stress-strain curve of high strength steel and plastic analysis, respectively. A large scale test and a series of non-linear finite element analysis for the continuous composite I-girder with high strength steel were then conducted to examine the effectiveness of proposed models and to investigate the effect of high strength steel on the inelastic behavior of the negative bending moment region of the continuous composite I-girder with high strength steel. Finally, it can be found that the proposed equations provided good estimation of the requited and available rotation capacity of the continuous composite I-girder with high strength steel.

Experimental and analytical investigation of composite columns made of high strength steel and high strength concrete

Binglin Lai,J.Y. Richard Liew,Mingxiang Xiong 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.1

Composite columns made of high strength materials have been used in high-rise construction owing to its excellent structural performance resulting in smaller cross-sectional sizes. However, due to the limited understanding of its structural response, current design codes do not allow the use of high strength materials beyond a certain strength limit. This paper reports additional test data, analytical and numerical studies leading to a new design method to predict the ultimate resistance of composite columns made of high strength steel and high strength concrete. Based on previous study on high strength concrete filled steel tubular members and ongoing work on high strength concrete encased steel columns, this paper provides new findings and presents the feasibility of using high strength steel and high strength concrete for general double symmetric composite columns. A nonlinear finite element model has been developed to capture the composite beam-column behavior. The Eurocode 4 approach of designing composite columns is examined by comparing the test data with results obtained from code's predictions and finite element analysis, from which the validities of the concrete confinement effect and plastic design method are discussed. Eurocode 4 method is found to overestimate the resistance of concrete encased composite columns when ultra-high strength steel is used. Finally, a strain compatibility method is proposed as a modification of existing Eurocode 4 method to give reasonable prediction of the ultimate strength of concrete encased beam-columns with steel strength up to 900 MPa and concrete strength up to 100 MPa.

Structural Performance of 800 MPa High-Strength Steel Members and Application to Highrise and Mega Building Structures

Lee, Cheol-Ho Council on Tall Building and Urban Habitat Korea 2017 International journal of high-rise buildings Vol.6 No.3

The use of high-strength steels in construction of highrise and mega building structures can bring about many technological advantages from fabrication to erection. However, key design criteria such as local and lateral stability in current steel design specifications were developed based on tests of ordinary steels which have stress-strain characteristics very different from that of high strength steels. A series of tests on 800 MPa tensile strength steel (HSA800) members are summarized in this paper which were conducted to investigate the appropriateness of extrapolating current ordinary-steel based design criteria to high strength steels. 800 MPa I-shape beam specimens designed according to flange local buckling (FLB) criteria of the AISC Specification developed a sufficient strength for elastic design and a marginal rotation capacity for plastic design. It is shown that, without introducing distinct and significant yield plateau to the stress-strain property of high-strength steel, it is inherently difficult to achieve a high rotation capacity even if all the current stability limits are met. 800 MPa I-shape beam specimens with both low and high warping rigidity exhibited sufficient lateral torsional buckling (LTB) strength. HSA800 short-column specimens with various edge restraint exhibited sufficient local buckling strength under uniform compression and generally outperformed ordinary steel specimens. The experimental P-M strength was much higher than the AISC nominal P-M strength. The measured residual stresses indicated that the impact of residual stress on inelastic buckling of high-strength steel is less. Cyclic seismic test results showed that HSA800 members have the potential to be used as non-ductile members or members with limited ductility demand in seismic load resisting systems. Finally, recent applications of 800 MPa high strength steel to highrise and mega building structures in Korea are briefly presented.

주관응력효과를 고려한 고강도강 X형 원형강관접합부의 수치해석 연구

김선후,이철호 한국강구조학회 2018 韓國鋼構造學會 論文集 Vol.30 No.2

Internationally representative steel design standards have forbidden or limited the application of high-strength steels to tubular joints, partly because of concerns about their unique material characteristics such as high yield ratio. Most of design standards stipulate that for steels whose yield strengths exceed 355 or 360 MPa, the strength equations cannot be utilized or strength reduction factor below 1.0 should be multiplied. However, the mechanical background behind these limitations is not clear. Experimental testing of high-strength steel CHS (circular hollow section) X-joints recently conducted by the authors also clearly indicated that the current limitations might be unduly conservative. As a continuing work, extensive, test-validated numerical analyses were made to investigate the behavior of high-strength steel CHS X-joint under axial compression. Three steel grades covering ordinary to very high strength steels were considered in the analysis. Again it was found that the high strength penalty to the joint strength in current standards is too severe and needs to be relaxed. The high-strength steel joints under the effects of chord stress generally showed higher strength than the ordinary steel joints and their strengths were conservatively predicted by current standards. It is also emphasized that current format of the CHS X-joint strength equation does not reflect observed behavior and needs to be recast. 고강도 강재의 높은 항복비와 같은 특이한 물성에 대한 우려 등의 이유로 국내외 대표적인 강구조 설계기준에서는 강관구조에 고강도강재를 적용하는 것을 금지하거나 제한하고 있다. 대부분의 설계기준에서는 강관의 항복강도가 355 또는 360MPa을 초과하는 경우 제시된 설계강도식을 사용할 수 없거나 강도저감계수를 통해 설계강도를 낮추어야 한다. 반면 이러한 제한사항에 대한 역학적 근거는 명료하지 않다. 또한 최근 저자들에의해 수행된 X형 원형강관접합부에 대한 실험연구는 고강도강에 대한 규제가 과도하게 보수적일 수도 있다는 점을 지적한 바 있다. 본 연구에서는고강도강 X형 원형강관접합부의 지관 압축 하에서의 거동을 더 자세히 분석하기 위해 실험에 이은 수치해석 변수연구를 수행하였다. 일반 강재부터매우 항복강도가 높은 고강도 강재까지 넓은 범위의 강종을 고려하였다. 본 수치해석 연구에서도 현행의 고강도강 페널티가 매우 보수적이며 완화될여지가 있음을 확인할 수 있었다. 또한 주관 축응력 하에서의 고강도강 접합부의 거동을 분석한 결과 현행 기준식이 고강도강 접합부의 주관 축응력에의한 강도 감소 효과를 보수적으로 예측함을 확인하였다. 일반적으로 주관 축응력이 작용할 때 고강도강 접합부는 일반강 접합부에 비해 접합부 강도를 더 잘 유지하였다. 더불어 현행 기준식의 형태가 실제 접합부 거동을 정확히 표현하는 데에 한계가 있으며 개선될 여지가 있음을 지적하였다.

Flexural behavior of high-strength steel hybrid composite beams

Jun, Su-Chan,Lee, Cheol-Ho,Han, Kyu-Hong,Kim, Jin-Won Elsevier 2018 Journal of constructional steel research Vol.149 No.-

<P><B>Abstract</B></P> <P>In this study, hybrid utilization of high-strength steel in composite beams was proposed in order to maximize their flexural capacity and full-scale testing was conducted in two phases to investigate their flexural behavior. In fabricating specimens, high-strength steels were utilized for the bottom flange while normal-strength steels were used for the top flange and the web. In Phase I testing, however, all the high-strength steel bottom flange specimens were not able to reach their plastic moment by about 10–15% due to unexpected longitudinal shear failure along the beam axis, although sufficient shear studs were provided for full composite behavior and the plastic neutral axis location was limited within 15% of the total depth of the composite beam section. The specimens in Phase II testing designed with additional shear reinforcements showed no longitudinal shear cracking and developed their plastic capacity with reasonable deformability as intended in design. This implies that, different from the design of conventional composite beams, checking the longitudinal shear strength of composite concrete slab is crucial when designing hybrid composite beams utilizing high-strength steels. The nominal longitudinal shear strength was well predicted by the shear-friction based models in ACI 318-14 and AASHTO LRFD. The test results of this study show that when the limitation on the depth of the plastic neutral axis set forth by Eurocode 4 is satisfied along with sufficient longitudinal shear strength, the plastic stress design method can still be applied to the design of hybrid composite beams utilizing high-strength steels whose nominal yield strength is as high as 650 MPa.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hybrid utilization of high-strength steel in composite beams to maximize their flexural capacity is presented. </LI> <LI> The longitudinal shear failure of the concrete slab is one of the critical limit states in hybrid composite beams. </LI> <LI> The reliability of the design equations for the longitudinal shear strength among representative standards is evaluated. </LI> <LI> The plastic stress design method can still be applied to high-strength hybrid composite beams. </LI> </UL> </P>

휨을 받는 강섬유 보강 고강도철근 콘크리트 보의 구조 거동

양인환,김경철,조창빈 한국구조물진단유지관리공학회 2016 한국구조물진단유지관리공학회 논문집 Vol.20 No.3

The purpose of this paper is to investigate the flexural behavior of high-strength steel fiber-reinforced concrete beams with compressive strength of 130 MPa. The paper presents experimental research results of steel fiber-reinforced concrete beams with steel fiber content of 1.0% by volume and steel reinforcement ratio of less than 0.02. Both of normal-strength rebar and high-strength rebar were used in the test beams. Modeling as well as compressive and tensile strength test of high-strength steel fiber- reinforced concrete was performed to predict the bending strength of concrete beams. Tension modeling was performed by using inverse analysis in which load-crack mouth opening displacement relationship was considered. The experimental results show that high-strength steel fiber-reinforced concrete beams and the addition of high-strength rebar is in favor of cracking resistance and ductile behavior of beams. For beams reinforced with normal-strength rebar, the ratio of bending strength prediction to the test result ranged from 0.81 to 1.42, whereas for beams reinforced with high-strength rebar, the ratio of bending strength prediction to the test result ranged from 0.92 to 1.07. The comparison of bending strength from numerical analysis with the test results showed a reasonable agreement. 이 논문의 목적은 압축강도 130 MPa급의 고강도 강섬유 보강 콘크리트 보의 휨거동 특성을 파악하는데 있다. 부피비 1.0%의 강섬유와 철근비 0.02 이하의 철근으로 보강된 고강도 강섬유 보강 콘크리트의 휨거동 특성 실험결과를 제시하였다. 일반강도철근과 고강도철근을 실험 부재에 사용하였다. 강섬유 보강 콘크리트의 압축 및 인장거동 재료 실험과 모델링을 수행하였다. 강섬유 보강 콘크리트의 하중-균열개구변위 실험결과를 반영하여 가상균열모델에 근거한 역해석을 통해 인장거동모델링을 제시하였다. 실험결과는 강섬유 보강 콘크리트와 고강도철근의 사용은 균열제어 및 연성 거동에 유리한 것을 나타낸다. 일반강도철근을 사용한 보의 휨강도 실험값에 대한 수치해석에 의한 예측값의 비는 0.81~1.42를 나타내고, 고강도철근을 사용한 보의 휨강도 실험값에 대한 수치해석에 의한 예측값의 비는 0.92~1.07을 나타낸다. 수치해석에 의한 휨강도는 실험결과를 합리적으로 예측하고 있는 것으로 판단된다.

Experimental and analytical investigation of high-strength concrete-filled steel tube square columns subjected to flexural loading

유정한,Kyung-Soo Chung,Jin-Ho Kim 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.14 No.2

The concrete-filled steel tube (CFT) columns have several benefits of high load-bearing capacity, inherent ductility and toughness because of the confinement effect of the steel tube on concrete and the restraining effect of the concrete on local buckling of steel tube. However, the experimental research into the behavior of square CFT columns consisting of high-strength steel and high-strength concrete is limited. Six full scale CFT specimens were tested under flexural moment. The CFT columns consisted of high-strength steel tubes (fy = 325 MPa, 555 MPa, 900 MPa) and high-strength concrete (fck = 80 MPa and 120 MPa). The ultimate capacity of high strength square CFT columns was compared with AISC-LRFD design code. Also,this study was focused on investigating the effect of high-strength materials on the structural behavior and the mathematical models of the steel tube and concrete. Nonlinear fiber element analyses were conducted based on the material model considering the cyclic bending behavior of high-strength CFT members. The results obtained from the numerical analyses were compared with the experimental results. It was found that the numerical analysis results agree well with the experimental results.

Dynamic Response of High Strength Steel Beams Subjected to Explosion Induced Blast Load

Xinchang Feng,Xiyue Liu,Zhiyang He,Shuxin Bai,Shun Li,Yu Tang 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.6

A series of anti-explosion tests were performed on H-type high strength steels (Q460JSC and HQ600) and ordinary steels (Q345B) to address the problem of anti-explosion in the technical application of high strength steel. The dynamic behavior of steel beams during explosion and the propagation of shock waves were analyzed. The effects of proportionate distance, steel strength, high-span ratio, section shapes were investigated. The finite element software (ANSYS/LS-DYNA) was used to analyze the anti-explosion performance of high strength steel beams. The finite element models which adopted modified Johnson–Cook constitutive model and damage criterion were validated by comparing with the experimental results. The influence factors of anti-explosion performance of high strength steel were explored by numerical simulation as well. The results reveal that under near-explosion conditions, the peak values of overpressure predicted by empirical formulas are often less than the experimental outcomes. As the scaled distance reduces, the damage to the steel beam increases, making it more prone to local fracture. By decreasing the scaled distance, increasing the high-span ratio, and strengthening the constraint of H-type steel beam, the deformation and damage of steel beams can reduce. The results provide an effective basis to evaluate the safety of high strength steel beams applied in practical engineering when subjected to explosion.