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BEHAVIOR AND DESIGN OF COMPOSITE PLATE SHEAR WALLS/CONCRETE FILLED UNDER FIRE LOADING
No full textComposite Plate Shear Walls - Concrete Filled (C-PSW/CF), also known as SpeedCore walls, are increasingly used in commercial buildings. C-PSW/CF offer the advantages of modularization and expedited construction time. The performance of C-PSW/CF under wind and seismic loading has been extensively studied. As such, building codes permit the use of these walls in non-seismic and seismic regions. In addition to these lateral loads, C-PSW/CF may be exposed to fire loading during their service life. Elevated temperatures resulting from the fire loading subject structural components to a set of forces and deformations. These elevated temperatures result in the significant degradation of the material properties. Thus, fire loading may lead to the failure of structural components during fire incidents within the buildings.
This dissertation describes (i) experimental, numerical, and analytical studies conducted to evaluate the performance of C-PSW/CF and (ii) the development of design guidelines for C-PSW/CF subjected to fire and gravity loading. The results from prior experimental investigations were compiled, and five additional fire tests were conducted to address gaps in the experimental data. The fire tests were conducted on laboratory-scale specimens subjected to axial compressive loading and simulated standard fire loading (heating). The parameters considered in the tests were axial compressive loading (21% – 30% of section compressive strength, Ag f’c), steel plate slenderness (24 – 48, tie spacing-to-steel plate thickness ratio), and uniformity of heating (all-sided versus three-sided heating).
Numerical and analytical studies were conducted using two independent methods namely Finite Element (FE) and Finite Difference (FD) methods. The developed models were benchmarked to test data, and the benchmarked models were used to conduct parametric studies to expand the database. The thermal and structural material properties recommended by Eurocode standards were applied in these models. The parameters considered were the wall thickness (200 mm – 600 mm), wall slenderness (story height-to-concrete thickness ratio, H/tc= 5 – 25), axial load ratio (Pu ≤ 30% section concrete strength, Ac f’c), heating uniformity (uniform versus non-uniform heating), boundary conditions (pinned versus fixed), cross-sectional steel plate reinforcement ratio (As/Ag =1.3% – 5.3%), steel plate slenderness ratio (stie/tp = 20 – 75), tie bar spacing-to-wall concrete thickness ratio (stie/tc = 0.5 – 1.0), and concrete compressive strength (f’c = 40 MPa – 55 MPa).
Symmetric nonlinear thermal gradients were developed through wall thickness for the walls exposed to uniform fire loading. Due to the low thermal conductivity of concrete, the temperature decreased nonlinearly through the wall thickness towards the mid-thickness of the walls. For the non-uniform fire exposure, temperatures through the wall thickness decreased nonlinearly towards the unexposed surface of the walls. A consistent trend was observed in the axial displacements of C-PSW/CF under combined fire and gravity loading. The observed trend consisted of several steps including (i) thermal expansion, (ii) gradual axial shortening, (iii) fast axial shortening, and (iv) failure.
Local buckling of steel plates between tie bars was observed in all walls. However, this phenomenon did not cause any significant degradation in structural performance or failure of the walls. The results from parametric studies indicated that wall slenderness ratio (story height-to-wall thickness ratio), wall thickness, applied axial load ratio, and end boundary conditions have a significant influence on the fire resistance of C-PSW/CF. Higher wall slenderness ratios and load ratios had a detrimental effect on the fire resistance of walls. Global buckling was the dominant failure mode for the walls with high slenderness ratios (e.g., H/tc ³ 15). In thicker walls, the lower temperatures in the middle regions of the concrete helped to maintain the axial compressive capacity of walls under fire loading. Limiting the steel plate slenderness ratio could slightly improve the fire resistance of unprotected walls by arresting the extent of local buckling between tie bars.
The results from the parametric studies have been used to develop an approach for designing C-PSW/CF subjected to combined fire and gravity loading. The total (linear) length of the wall was discretized into unit width columns, where each unit width column corresponded to a length of wall equal to the tie bar spacing (stie). Thus, each unit is like a column with steel plates on two opposite surfaces, concrete infill, and tie bars distributed uniformly along the height. The axial load capacity of C-PSW/CF can be estimated as the axial load capacity of the unit width column, calculated using the developed approach, multiplied by the linear length of the wall divided by the unit width (tie bar spacing). For this approach, the wall slenderness ratio (H/tw), has a limiting value of 20. Walls with wall slenderness ratios greater than 20 should be fire protected. The expansion of the material on the exposed surface of walls generated moments through the wall cross-section in non-uniform fire scenarios. This phenomenon caused the early failure of walls (~40 minutes) with wall slenderness ratios greater than 20. An approach was developed to conservatively estimate the fire-resistance rating (in hours) of unprotected C-PSW/CF exposed to the standard fire time-temperature curve. The fire-resistance rating of C-PSW/CF depends directly on the applied axial load ratio, wall slenderness ratio, and wall thickness.
The temperature profile through the wall thickness can be calculated by discretizing the section into fibers (or elements). Since the temperature of the elements is uniform along the height and length of walls, 1D thermal analysis (through wall thickness) can be performed using heat transfer equations or the fiber-based program developed in the study.
Vent holes are recommended to relieve the buildup steam pressure as the moisture content of concrete evaporates at temperatures exceeding the boiling point of water. A rational method was developed to design the vent holes as a function of the maximum temperature and thermal gradient through the wall thickness, heating duration, moisture content, and the acceptable level of pressure buildup on the steel plates. However, in typical cases, unprotected C-PSW/CF walls can be provided with 25 mm diameter vent holes spaced at a distance equal to story height or 3.6 m (maximum) in the horizontal and vertical directions to relieve the buildup of steam or water vapor pressure.
This research study also led to the development and validation of a computer program that can be used instead of the design equations to more accurately model and calculate the thermal and structural performance of composite C-PSW/CF. This program is based on a fiber-based section and member analysis method that can be used to evaluate the performance and axial (gravity) load capacity of unprotected and protected C-PSW/CF subjected to uniform or non-uniform heating. The analysis can be conducted by implementing standard (ISO 834 or ASTM E119), Eurocode parametric, or user input gas (or surface) time-temperature curves.
The proposed equations and the recommendations in this study can be used to develop design guidelines and specifications for fire resistance design of C-PSW/CF under combined fire and gravity loading. A code change proposal will be proposed to AISC Specification - Appendix 4 (Structural Design for Fire Condition).</p
Effectiveness of Damaged Fireproofing in Structural Steel Members Subjected to Fire
No full textFire incidents and elevated temperatures reduce the strength of structural steel members significantly. Passive fireproofing is a common method to protect steel structures against fire. In passive fireproofing method, a fire protection material is applied to structural members and connections to delay the heat transfer to steel in order to increase its fire resistance. However, during the service life of a structure, the fireproofing material may be damaged or removed due to accidents, improper applications or by connecting steel members to each other, which may happen after applying the fireproofing material. High thermal conductivity of steel material allows a fast spread of high temperature through the structural element at damaged regions. The concrete encasement is a typical passive fireproofing material to protect steel structures in oil and gas refineries and petrochemical plants. This study is focused on investigating the effect of the damaged concrete fireproofing on the structural response of structural steel members. Cases with different damage length, shapes and, penetration were studied to investigate the impact of such damages on the members’ structural response. Thermal and structural nonlinear finite elements analysis were performed. Finite element models were validated with experimental results from a published literature. Structural response of the damaged fireproofed beams was compared with the response of the fully protected beams subjected to ASTM E119 standard fire temperature. The deflection and strength failure limit states were investigated to determine the fire resistance of each studied case. It was observed that minor loss in fireproofing material dramatically reduces the fire resistance of the steel members. Damage length, size of beam and post-damaged fireproofing thickness influence the fire resistance of beams with damaged concrete fireproofing
Effectiveness of Damaged Fireproofing in Structural Steel Members Subjected to Fire
No full textFire incidents and elevated temperatures reduce the strength of structural steel members significantly. Passive fireproofing is a common method to protect steel structures against fire. In passive fireproofing method, a fire protection material is applied to structural members and connections to delay the heat transfer to steel in order to increase its fire resistance. However, during the service life of a structure, the fireproofing material may be damaged or removed due to accidents, improper applications or by connecting steel members to each other, which may happen after applying the fireproofing material. High thermal conductivity of steel material allows a fast spread of high temperature through the structural element at damaged regions. The concrete encasement is a typical passive fireproofing material to protect steel structures in oil and gas refineries and petrochemical plants. This study is focused on investigating the effect of the damaged concrete fireproofing on the structural response of structural steel members. Cases with different damage length, shapes and, penetration were studied to investigate the impact of such damages on the members’ structural response. Thermal and structural nonlinear finite elements analysis were performed. Finite element models were validated with experimental results from a published literature. Structural response of the damaged fireproofed beams was compared with the response of the fully protected beams subjected to ASTM E119 standard fire temperature. The deflection and strength failure limit states were investigated to determine the fire resistance of each studied case. It was observed that minor loss in fireproofing material dramatically reduces the fire resistance of the steel members. Damage length, size of beam and post-damaged fireproofing thickness influence the fire resistance of beams with damaged concrete fireproofing
Lessons Learned from the Deadliest Earthquake of 2017: Study of Damage and the Crisis Response Preparedness
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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