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CONTENTS
Volume 43, Number 3, May10 2022 (Special Issue)
 

Abstract
A variety of research methods are applied for gaining an understanding of the behavior and failure of steel and composite infrastructures. Experimental, numerical and analytical investigations are some of the conventional and powerful research methods. Field & forensic monitoring, non-destructive research and statistical or data-driven approaches are also getting more attention these days. All of such methods that focus on the steel and composite infrastructures are included in this special issue of Steel and Composite Structures: An International Journal, with more of a focus on forensic investigation and engineering. Forensic engineering of infrastructure is the application of engineering knowledge to the investigation of failure, collapse and other performance problems of construction facilities and built environments. Due to various geometric and material complexibility, it is very hard to investigate the causes, mechanism, and scenario of the failure and collapse of various infrastructures which may result in serious damage to society. For more precise investigation of the accidents and effective execution planning against the failures, advanced forensic engineering and its application based on innovative sensing, analysis, and experiment are required. The purposes of the special issue are to introduce analyses and experiments related to the (forensic) engineering of composite super-structures, sub-structures, and integrated infrastructures, and to promote the forensic practice. All the papers by renowned authors were reviewed by peer scholars and practitioners. An emphasis of the special issue was on research methods relevant to forensic investigation of hyper-converged infrastructure.

Key Words


Address


Abstract
Accurate design models for predicting the shear resistance of headed studs in solid concrete slabs are essential for obtaining economical and safe steel-concrete composite structures. In this study, symbolic regression with genetic programming (GPSR) was applied to experimental data to formulate new descriptive equations for predicting the shear resistance of studs in solid slabs using both normal and lightweight concrete. The obtained GPSR-based nominal resistance equations demonstrated good agreement with the test results. The equations indicate that the stud shear resistance is insensitive to the secant modulus of elasticity of concrete, which has been included in many international standards following the pioneering work of Ollgaard et al. In contrast, it increases when the stud height-to-diameter ratio increases, which is not reflected by the design models in the current international standards. The nominal resistance equations were subsequently refined for use in design from reliability analyses to ensure that the target reliability index required by the Eurocodes was achieved. Resistance factors for the developed equations were also determined following US design practice. The stud shear resistance predicted by the proposed models was compared with the predictions from 13 existing models. The accuracy of the developed models exceeds the accuracy of the existing equations. The proposed models produce predictions that can be used with confidence in design, while providing significantly higher stud resistances for certain combinations of variables than those computed with the existing equations given by many standards.

Key Words
genetic programming; headed studs; machine learning; reliability; shear resistance; steel-concrete composite structures; symbolic regression

Address
Vitaliy V. Degtyarev:New Millennium Building Systems, Columbia, SC, U.S.A.

Stephen J. Hicks:School of Engineering, University of Warwick, Coventry, CV4 7AL, U.K.

Jerome F. Hajjar:Department of Civil and Environmental Engineering, Northeastern University, Boston, MA, U.S.A.

Abstract
For multi-story structural systems, Korean steel industry has fostered development of a steel-concrete composite beam. Configuration of the composite beam is characterized by steel angle shear connectors welded to a U-shaped cold formedsteel beam. Effects of shear connector orientation and spacing were studied to evaluate current application of the angle shear connector design equation in AC495. For the study, interfacial shear resistance behavior was investigated by conducting 24 push-out tests and attuned using unreinforced push-out specimens. Interfacial shear to horizontal slip response was reported along with corresponding failure patterns. Pure shear connector strength was also evaluated by excluding concrete shear contribution, which was estimated in relation to steel beam-slab interface separation or interfacial crack width.

Key Words
aggregate interlocking resistance; angle; channel; cold formed-steel; composite beam; concrete; interfacial shear strength; push-out test; shear connector; U-shaped section

Address
Hyoung Seok Oh:Department of Architecture and Architectural Engineering, Seoul National University,
1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

Hyeongyeop Shin:Department of Architecture and Architectural Engineering, Seoul National University,
1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

Youngkyu Ju:Department of Civil, Environmental and Architectural Engineering, Korea University,
145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea

Thomas H.-K. Kang:Department of Architecture and Architectural Engineering, Seoul National University,
1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

Abstract
A vast amount of experimental and analytical research has been conducted related to the seismic behavior and performance of concrete filled steel tubular (CFT) columns. This research has resulted in a wealth of information on the component behavior. However, analytical and experimental data for structural systems with CFT columns is limited, and the well-known behavior of steel or concrete structures is assumed valid for designing these systems. This paper presents the development of an analytical model for nonlinear analysis of composite moment resisting frame (CFT-MRF) systems with CFT columns and steel wide-flange (WF) beams under seismic loading. The model integrates component models for steel WF beams, CFT columns, connections between CFT columns and WF beams, and CFT panel zones. These component models account for nonlinear behavior due to steel yielding and local buckling in the beams and columns, concrete cracking and crushing in the columns, and yielding of panel zones and connections. Component tests were used to validate the component models. The model for a CFT-MRF considers second order geometric effects from the gravity load bearing system using a lean-on column. The experimental results from the testing of a four-story CFT-MRF test structure are used as a benchmark to validate the modeling procedure. An analytical model of the test structure was created using the modeling procedure and imposeddisplacement analyses were used to reproduce the tests with the analytical model of the test structure. Good agreement was found at the global and local level. The model reproduced reasonably well the story shear-story drift response as well as the column, beam and connection moment-rotation response, but overpredicted the inelastic deformation of the panel zone.

Key Words
analytical models; composite moment resisting frames; concrete filled tube columns; earthquake resistant structures; high strength concretel; high strength steel; nonlinear analysis; steel wide flange beams

Address
Ricardo A. Herrera:Dept of Civil Engineering, University of Chile, Av. Blanco Encalada 2002, Piso 4, 8370449 Santiago, Chile

Teerawut Muhummud:Dept of Civil Technology Education, King Mongkut

Abstract
This paper presents an inelastic buckling behavior analysis of rectangular hollow steel tubes with geometrical imperfections under elevated temperatures. The main variables are the temperature loads, slenderness ratios, and exposure conditions at high temperatures. The material and structural properties of steels at different temperatures are based on Eurocode (EN 1993-1-2, 2005). In the elastic buckling analysis, the buckling strength decreases linearly with the exposure conditions, whereas the inelastic buckling analysis shows that the buckling strength decreases in clusters based on the exposure conditions of strong and weak axes. The buckling shape of the rectangular steel column in the elastic buckling mode, which depicts geometrical imperfection, shows a shift in the position at which bending buckling occurs when the lower section of the member is exposed to high temperatures. Furthermore, lateral torsional buckling occurs owing to cross-section deformation when the strong axial plane of the model is exposed to high temperatures. The elastic buckling analysis indicates a conservative value when the model is exposed to a relatively low temperature, whereas the inelastic buckling analysis indicates a conservative value at a certain temperature or higher. The comparative results between the inelastic buckling analysis and Eurocode 3 show that a range exists in which the buckling strength in the design equation result is overestimated at elevated temperatures, and the shapes of the buckling curves are different.

Key Words
elevated temperature; finite element analysis; nonlinear buckling; rectangular hollow section; slenderness ratio

Address
Jihye Seo:Ocean Engineering Research Division, Korea Institute of Ocean Science and Technology,
385, Haeyang-ro, Yeongdo-gu, Busan 49111, Republic of Korea

Deokhee Won:Department of Civil Engineering, Halla University, 28, Halladae-gil, Heungeop-myeon, Wonju-si, Gangwon-do 26404, Republic of Korea

Seungjun Kim:School of Civil, Environmental and Architectural Engineering, Korea University, 145, Anam-ro, Seongbuk-gu,Seoul 02841, Republic of Korea

Abstract
Bridge fire hazard has become a growing concern over the last decade due to the rapid increase of ground transportation of hazardous materials and resulting fire incidents. The lack of fire safety provisions in steel bridges can be a significant issue owing steel thermal properties that lead to fast degradation of steel properties at elevated temperatures. Alternatively, the development of composite action between steel girders and concrete decks can increase the fire resistance of steel bridges and meet fire safety requirements in some applications. This paper reviews the fire problem in steel bridges and the fire behavior of composite steel-concrete bridge girders. A numerical model is developed to trace the fire response of a typical bridge girder and is validated using measurements from fire tests. The selected bridge girder is composed by a hot rolled steel section strengthened with bearing stiffeners at midspan and supports. A concrete slab sitting on the top of the girder is connected to the slab through shear studs to provide full composite action. The validated numerical model was used to investigate the fire resistance of real scale bridge girders and the effect of the composite action under different scenarios (standard and hydrocarbon fires). Results showed that composite action can significantly increase the fire resistance of steel bridge girders. Besides, fire severity played an important role in the fire behavior of composite girders and both factors should be taken into consideration in the design of steel bridges for fire safety.

Key Words
advanced analysis; bridge girders; composite structures; fire resistance; numerical models

Address
Venkatesh K.R. Kodur and Augusto Gil: Department of Civil and Environmental Engineering, Michigan State University,
3574 Engineering Building, 428 S. Shaw Lane, East Lansing/MI, USA - 48823


Abstract
As a key reinforcement connection between a tower and a substructure in offshore wind turbine system, the transition piece is inevitably subjected to cyclic dynamic environmental loads such as wind, current and wave. Therefore, well designed transition piece with high strength and good fatigue resistance is of great significance to the structural safety and reliability of offshore wind power systems. In this study, the structural behavior of the transition piece was studied by an extensive sets of finite element analyses. Three widely used types of transition piece were considered. The characteristics of stress development, fatigue life and weight depending on the type of the transition piece were investigated in the ultimate limit state (ULS) and the fatigue limit state (FLS) of a 5-MW offshore wind turbine to be placed in Korea. An optimal form of the transition piece was proposed based on this parametric study.

Key Words
finite element analysis; offshore wind turbine; optimal form; transition piece; ULS and FLS

Address
Chuan Ma and Goangseup Zi:School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 02841, Korea

Abstract
Nibellen structural system is a novel resilient bracing system based on the application of Bellville disks and Nitinol rods. The cyclic behavior of Nibellen assembly was obtained, and the design equations were developed based on the available literature. Seismic performance of the system was then studied analytically. Two groups of buildings with different lateral force resisting systems were designed and studied: one group with the Nibellen system, and the other with the special concentrically braced frame system. Each building group consisted of 5-, 10-, and 15-story buildings. The Design-Base-Event (DBE) and Maximum Considered Event (MCE) were considered as the seismic hazard, and a suite of seven ground motions were scaled accordingly for response history analyses. Finally, the resiliency of the buildings was studied by obtaining the functionality curve of the buildings before and after the seismic event. The construction cost of the 5-story building with Nibellen bracing system increased but the post-earthquake cost decreased significantly. The application of Nibellen system in the 10- and 15-story buildings reduced both the construction and repair costs, considerably. Resiliency of all the buildings was improved when Nibellen system was used as the lateral force resisting system.

Key Words
cost estimation; hazard analysis; nibellen system; resiliency; structural bracing system; special concentrically braced frame

Address
Alireza Asgari Hadad:GEI Consultants, Inc. 109 W. Baraga Avenue, 49855, Marquette, Michigan, USA

Bahram M Shahrooz:Department of Civil and Architectural Engineering and Construction Management, University of Cincinnati,
2600 Clifton Ave, 45221, Cincinnati, Ohio, USA

Abstract
This study investigated the flowability and mechanical properties of cost-effective steel fiber reinforced ultra-high performance concrete (UHPC) by using locally available materials for field-cast application. To examine the effect of mixture constituents, five mixtures with different fractions of silica fume, silica powder, ground granulated blast furnace slag (GGBS), silica sand, and crushed natural sand were proportionally prepared. Comprehensive experiments for different mixture designs were conducted to evaluate the fresh- and hardened-state properties of self-consolidating UHPC. The results showed that the proposed UHPC had similar mechanical properties compared with conventional UHPC while the flow retention over time was enhanced so that the field-cast application seemed appropriately cost-effective. The self-consolidating UHPC with high flowability and low viscosity takes less total mixing time than conventional UHPC up to 6.7 times. The X-ray computed tomographic imaging was performed to investigate the steel fiber distribution inside the UHPC by visualizing the spatial distribution of steel fibers well. Finally, the tensile stress-strain curve for the proposed UHPC was proposed for the implementation to the structural analysis and design.

Key Words
flowability; mechanical property; spatial distribution; steel fiber; tensile stress-strain curve; X-ray CT

Address
Jiho Moon:Department of Civil Engineering, Kangwon National University, Chuncheon 24341, Republic of Korea

Kwang Soo Youm:GS Construction & Engineering, 33 Jong-ro, Jongro-gu, Seoul 03159, Republic of Korea

Jong-Sub Lee:3School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 02841, Republic of Korea

Tae Sup Yun:School of Civil and Environmental Engineering, Yonsei-ro 50, Yonsei University, Seoul 03722, Republic of Korea

Abstract
Recently, there has been an increasing demand for buildings that allow rapid assembly of construction elements, have ample open space areas and are flexible in their final intended use. Accordingly, researchers have developed new competitive structures in terms of cost and efficiency, such as cold-formed steel and timber composite floors, to satisfy these requirements. Cold-formed steel and timber composite floors are light floors with relatively high stiffness, which allow for longer spans. As a result, they inherently have lower fundamental natural frequency and lower damping. Therefore, they are likely to undergo unwanted vibrations under the action of human activities such as walking. It is also quite expensive and complex to implement vibration control measures on problematic floors. In this study, a finite element model of a composite floor reported in the literature was developed and validated against four-point bending test results. The validated FE model was then utilised to examine the vibration behaviour of the investigated composite floor. Predictions obtained from the numerical model were compared against predictions from analytical formulas reported in the literature. Finally, the influence of various parameters on the vibration behaviour of the composite floor was studied and discussed.

Key Words
cold-formed steel; composite flooring systems; finite element method; floor vibrations; modal analysis; natural frequency

Address
Suleiman A. AL Hunaity, Harry Far and Ali Saleh: School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology,
University of Technology Sydney (UTS), Sydney, Australia

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