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Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 476-484). Available also in a digital version from Dissertation Abstracts.

When a building is exposed to fire, it is required to remain structurally stable for a period of time. The regulations do however allow some types of localised failures within this time frame. The damage area of these failures must be contained and remain proportional to the initial triggering action and not continue into a widespread collapse, commonly referred to as a progressive collapse. In order to prevent progressive collapses, it is necessary to first identify which types of failures that could result in a progressive collapse. In a recent study (Iqbal N., Ph.D. thesis, Luleå University of Technology, 2016), single-storey steel frame buildings affected by localised fires were analysed. In the study it was identified that an initial failure in the truss’ top chord could potentially result in a progressive collapse. The reason for this is because when the top chord fails, the truss and its roof sheeting deflect and transitions into only handling catenary forces. The catenary forces present in the roof sheeting are then transferred to the adjacent trusses which therefore risks collapsing. The analysis could however not determine the possibility of progressive collapses and how factors such as truss span length affect the possibility of progressive collapses. The purpose of this thesis therefore became to analyse how span length affect the roof sheeting’s catenary forces and try to determine if a failure in the top chord could result in a progressive collapse. To answer this, finite element analyses where conducted on two different truss models with varying span lengths, i.e. 18- and 36-meter. Each model consisted of three trusses along with columns, bracings, and roof sheeting. Additionally, a hand calculation model was adopted to determine the strength of the catenary forces. From the finite element analysis, it could be seen that the adjacent trusses of the 36-meter truss model became grossly deformed. Hence indicating that a longer span length would increase the possibility of a progressive collapse. However, the hand calculation model used to calculate the strength of the catenary forces indicated that catenary forces present in the roof sheeting of the longer truss model, was relatively weak compared to the shorter truss model. The reason for this could not be determined, but some adjustments to the hand calculation model might be necessary to make it compatible with the analysed truss model. Consequently, it was impossible to determine the possibility of a progressive collapse. Additionally, during this work it was identified that other factors, such as truss model, bay length and roof sheeting thickness, could affect the possibility of progressive collapses. Hence, further work is necessary to determine the possibility of a progressive collapse. / När en byggnad utsätts för brandpåverkan ska den förbli strukturellt stabil under en viss tidsperiod. Regelverken tillåter dock att vissa typer av lokala skador inträffar redan under denna tidsperiod. Dessa skador måste begränsas till en viss area och förbli proportionerliga mot den initiala skadan och inte resultera i utbredda kollapser, det vill säga fortskridande ras. För att kunna förhindra fortskridande ras är det nödvändigt att först identifiera vilka typer av skador som skulle kunna resultera i fortskridande ras.  I en relativt ny analys (Iqbal N., Doktorsavhandling, Luleå tekniska universitet, 2016) analyserades den bärande konstruktionen i enplans stålhallar då konstruktionen utsattes för lokala bränder. Där det identifierades att ett brott i balkens överram eventuellt skulle kunna resultera i ett fortskridande ras. Brottet i överramen medförde nämligen att balken och dess takplåt sjönk ihop och övergick till att endast hantera linkrafter. Takplåtens linkrafter fördelades ut till de angränsade balkarna som därmed riskerade att kollapsa. Analysen kunde dock inte verifiera att ett fortskridande ras var möjligt eller avgöra hur faktorer såsom balkspännvidd påverkade sannolikheten för ett fortskridande ras. Syftet med detta arbete blev därför att analysera om balkspännvidd påverkade takplåtens linkrafter samt att försöka avgöra om ett brott i överramen kan resultera i ett fortskridande ras eller inte. För att besvara detta genomfördes finita elementanalyser på en 18- och en 36-meter lång balk. Varje modell bestod av tre balkar med tillhörande pelare och takplåt. För att sedan kunna uppskatta styrkan av linkrafterna i takplåten tillämpades en handberäkningsmodell.  Resultatet från finita elementanalyserna visade att den längre balkmodellen utsattes för högre påkänningar i jämförelse med den kortare balkmodellen. Detta indikerar att en längre spännvidd ökar sannolikheten för fortskridande ras. Handberäkningsmodellen som användes för att beräkna styrkan av linkrafterna gav dock generellt mindre linkrafter för den längre balkmodellen jämfört med den kortare balkmodellen. Anledningen till detta gick inte att fastställa men det skulle kunna vara så att handberäkningsmodellen behöver justeras för att kunna tillämpas på den undersökta balkmodellen. I och med detta var det omöjligt att avgöra sannolikheten för ett fortskridande ras. Under detta arbete identifierades det även att andra faktorer så som balkmodell, centrumavstånd mellan fackverk och plåttakstjocklek skulle kunna påverka linkrafternas styrka. På grund av detta är fortsatt arbete nödvändigt för att kunna avgöra möjligheten och sannolikheten för ett fortskridande ras.

I arbetet undersöks behovet av ökad kontroll i stålbyggnadskonstruktioner med avseende på utförandefel. Riksdagen beslutade 1 juni 1994 att förändra Plan- och bygglagen (PBL) där förändringen trädde i kraft 1995 och bland annat innebar att hela ansvaret för en byggnads uppförande och kontroll lades på byggherren. Efter vintrarna 2009/10 och 2010/11 där flera tak rasade av snötyngden uppdagades en rad dimensionerings- och utförandefel. Under examensarbetet undersöktes vad som händer med säkerheten i byggnadskonstruktioner i stål som genomgår förändringar under dess livslängd och en jämförelse mot gällande regelverk genomfördes. En fältstudie och flera intervjuer genomfördes där fokus låg på utförandefel och hur förändringar av regelverk lett fram till dagens egenkontrollsystem som påverkat antalet utförandefel. Arbetets resultat visar att det kan finnas ett behov av att se över dagens kontrollsystem och att antalet allvarliga utförandefel i fallstudieobjektet ökat efter 1995. / In the work the need of increased inspections of steel structures with respect to errors of execution was examined. On 1 June 1994, the Swedish parliament decided to change the Planning and Building Act (PBL) and the changes came into force in 1995, where the entire responsibility for the construction and control of a building was placed on the developer. After the winters of 2009/10 and 2010/11, when several roofs collapsed by the snow weight, a number of design and execution faults were discovered. During the thesis work it was investigated what happens to the safety of building structures in steel that undergo changes during its lifetime and a comparison with current regulations was made. A field study and several interviews were conducted where the focus was on execution errors and how changes in regulations led to today's self-control systems that affect the number of execution errors. The results of the work show that there may be a need to review the current control system and that the number of serious execution errors in the case study object increased after 1995.

Observa-se no cenário mundial uma crescente tendência da construção de edifícios de aço. Assim, procurando encontrar a forma mais econômica para a construção, os edifícios projetados estão cada vez mais altos e seus elementos, vigas e pilares, formados por perfis cada vez mais leves. Com isso, são necessários estudos mais avançados para buscar um modelo estrutural que represente o comportamento real dessas estruturas. Este trabalho tem como objetivo discutir e propiciar uma melhor compreensão dos modelos e técnicas de análise estrutural aplicado aos edifícios de aço dando ênfase à influência das ligações. Foi realizado um aprimoramento dos modelos numéricos tridimensionais de ligações de aço e mistas. Foram analisadas três diferentes geometrias de edifícios considerando as não linearidades geométrica e do material, diferentes formas de representação das ligações, consideração das imperfeições geométricas iniciais e imperfeições iniciais de material. Estas análises foram feitas em modelos bidimensionais e tridimensionais. Observou-se grande diferença nos valores de esforços solicitantes e deslocamentos laterais quando a forma de consideração do comportamento semi-rígido das ligações foi variada. / It\'s possible to see that constructions of steel buildings in the world are increasing. Engineers have been trying to build economical constructions. So they have been designing tall buildings using light members. It is necessary new studies to develop structural models that represent structure\'s real behavior. The objective of this work is to discuss and to provide a better understanding of some models and technics used for design steel buildings. It was improved numerical three-dimensional models of steel connections and composite connections. It was analyzed three different geometry of building considering geometrical non-linearity, material non-linearity, different representation of connections, initial geometric imperfections, initial imperfections of material. These analyses were done on bidimensional and threedimensional models. It was noted big difference on internal forces and lateral displacement when was changed the way of representation of connections semi rigid behavior.

Observa-se no cenário mundial uma crescente tendência da construção de edifícios de aço. Assim, procurando encontrar a forma mais econômica para a construção, os edifícios projetados estão cada vez mais altos e seus elementos, vigas e pilares, formados por perfis cada vez mais leves. Com isso, são necessários estudos mais avançados para buscar um modelo estrutural que represente o comportamento real dessas estruturas. Este trabalho tem como objetivo discutir e propiciar uma melhor compreensão dos modelos e técnicas de análise estrutural aplicado aos edifícios de aço dando ênfase à influência das ligações. Foi realizado um aprimoramento dos modelos numéricos tridimensionais de ligações de aço e mistas. Foram analisadas três diferentes geometrias de edifícios considerando as não linearidades geométrica e do material, diferentes formas de representação das ligações, consideração das imperfeições geométricas iniciais e imperfeições iniciais de material. Estas análises foram feitas em modelos bidimensionais e tridimensionais. Observou-se grande diferença nos valores de esforços solicitantes e deslocamentos laterais quando a forma de consideração do comportamento semi-rígido das ligações foi variada. / It\'s possible to see that constructions of steel buildings in the world are increasing. Engineers have been trying to build economical constructions. So they have been designing tall buildings using light members. It is necessary new studies to develop structural models that represent structure\'s real behavior. The objective of this work is to discuss and to provide a better understanding of some models and technics used for design steel buildings. It was improved numerical three-dimensional models of steel connections and composite connections. It was analyzed three different geometry of building considering geometrical non-linearity, material non-linearity, different representation of connections, initial geometric imperfections, initial imperfections of material. These analyses were done on bidimensional and threedimensional models. It was noted big difference on internal forces and lateral displacement when was changed the way of representation of connections semi rigid behavior.

This dissertation discusses the potential for using a conventional main lateral-force resisting system, combined with the reserve strength in the gravity framing, and or auxiliary collapse-inhibiting mechanisms deployed throughout the building, or enhanced shear tab connections, to provide adequate serviceability performance and collapse safety for seismic and wind hazards in the central and eastern United States. While the proposed concept is likely applicable to building structures of all materials, the focus of this study is on structural steel-frame buildings using either non-ductile moment frames with fully-restrained flange welded connections not specifically detailed for seismic resistance, or ductile moment frames with reduced beam section connections designed for moderate seismic demands. The research shows that collapse prevention systems were effective at reducing the conditional probability of seismic collapse during Maximum Considered Earthquake (MCE) level ground motions, and at lowering the seismic and wind collapse risk of a building with moment frames not specifically detailed for seismic resistance. Reserve lateral strength in gravity framing, including the shear tab connections was a significant factor. The pattern of collapse prevention component failure depended on the type of loading, archetype building, and type of collapse prevention system, but most story collapse mechanisms formed in the lower stories of the building. Collapse prevention devices usually did not change the story failure mechanism of the building. Collapse prevention systems with energy dissipation devices contributed to a significant reduction in both repair cost and downtime. Resilience contour plots showed that reserve lateral strength in the gravity framing was effective at reducing recovery time, but less effective at reducing the associated economic losses. A conventional lateral force resisting system or a collapse prevention system with a highly ductile moment frame would be required for regions of higher seismicity or exposed to high hurricane wind speeds, but buildings with collapse prevention systems were adequate for many regions in the central and eastern United States. / Ph. D.

Stål är ett vanligt förekommande konstruktionsmaterial som används i olika typer av byggnader. Det är ett material med vilket klena dimensioner kan användas för att åstadkomma stora spännvidder och fria ytor. Däremot mjuknar stål vid höga temperaturer vilket kan innebära allvarliga skador i form av kollaps. I förebyggande syfte är det därför viktigt att brandskydda stålkonstruktioner på ett korrekt sätt. Syftet med detta examensarbete har varit att undersöka vilket brandskydd som är mest kostnadseffektivt genom att jämföra olika brandskydd som tillämpas i industrihallar. Studien har utförts i samarbete med Blixthuset Stålhallar och innefattar ett av deras pågående projekt där branddimensionering behövde utföras. Brandskydden som har jämförts är överdimensionering av stålprofil VKR 250X250X10, brandskivor, brandmålning och brandisolering. Initialt har lasteffekten i rumstemperatur beräknats i enlighet med Eurokoderna. Därefter har lasteffekten i brandlastfallet beräknats, följt av att den kritiska ståltemperaturen tagits fram på respektive våningsplan för både mittpelare och fasadpelare. Vid jämförelse av lasteffekterna som beräknats fram har utnyttjandegraden identifierats och därmed har behovet av brandskydd blivit känt. När den kritiska ståltemperaturen och utnyttjandegraden har fåtts fram har offerter från företag kunnat efterfrågas och en kostnadsjämförelse har därmed blivit möjlig. Studien har visat att överdimensionering av stålpelare inte är en effektiv lösning då inte ens den tjockaste profilen VKR 400X400X16 var tillräcklig tjock för att uppnå brandkravet R60. Trots överdimensionering hade stålpelarna behövt ytterligare brandskydd för att klara av brandkravet. Det dyraste brandskyddet var montering av brandskivor, följt av brandmålning och brandisolering. / Steel is a commonly used construction material. It is a material where small dimensions can be used to achieve large spans and free spaces. Steel softens however when encountering high temperatures which can cause severe damage such as collapses. It is therefore with greatest importance that fire protection is designed correctly. This bachelor thesis contains a study that compares different fire protections for industrialbuildings in steel, and the purpose of the study was to find the most economic efficient fire protection. This study has been made in collaboration with Blixthuset Stålhallar where one of their projects needed fire protection to be designed. The fire protections being compared was over dimensioning steel column VKR 250X250X10, using fire gips, fire insulation and fire painting. Initially, the load effect in room temperature was designed according to the Eurocodes. Thereafter, the load effect in the fire load case was designed, followed by finding the critical steel temperature. When comparing the two load effects, the utilization could be recognized and consequently, the requisite of fire protection could be identified. When the amount of fire protection needed was determined, offers from different companies could be taken in for comparison. The study showed that oversizing is an inefficient solution of fire protecting the steel columns since even the thickest steel column VKR 400X400X16 was not thick enough to achieve the fire requirement R60. Despite oversizing the steel columns, other fire protection would still be needed. Furthermore, the study showed that the most expensive fire protection wasassembly of fire discs, followed by fire painting. The cheapest alternative was fire insulation.

Este trabalho apresenta uma análise comparativa de diferentes sistemas estruturais para um edifício de 20 pavimentos. Cada um dos modelos foi dimensionado através dos princípios do método da análise direta, presente na ABNT NBR 8800:2008. O método da amplificação dos esforços solicitantes (MAES) foi usado para se obter de forma simplificada os esforços atuantes nos elementos do edifício considerando os efeitos locais e globais de segunda ordem. A incidência do vento foi simulada de duas formas diferentes. Na primeira, chamada de uniforme, o vento foi aplicado sem excentricidade, gerando apenas o efeito de tombamento nas estruturas. Na segunda hipótese, considerou-se uma excentricidade devida aos efeitos de vizinhança, prescrita pela ABNT NBR 6123:1988, responsável por ocasionar o tombamento e a torção dos edifícios. Todas as análises numéricas foram repetidas fazendo o uso de outro método simplificado de segunda ordem, conhecido como P-Delta. Por meio dos resultados obtidos, constatou-se que a possibilidade de se reduzir a sobrecarga para o dimensionamento de pilares proporciona uma economia de material, mas, por outro lado, tem como consequência o aumento do tempo de análise, pois exige a utilização de diferentes combinações de cálculo para o dimensionamento de vigas e pilares. A estratégia utilizada para simular os efeitos de vizinhança mostrou-se satisfatória, pois permitiu introduzir de maneira fácil e prática a torção ocasionada pela incidência excêntrica do vento. Observou-se também que esses efeitos ocasionaram o aumento dos momentos fletores e dos deslocamentos das estruturas analisadas. Em relação à avaliação dos efeitos de segunda ordem, comprovou-se que, para a classificação da deslocabilidade, a combinação de cálculo crítica é aquela que possui o maior carregamento gravitacional. Entretanto, para o dimensionamento dos elementos, foi constatado que outras hipóteses de cálculo, principalmente aquelas em que o vento é a ação variável principal, podem ser determinantes. Por fim, foi observado que os resultados obtidos pelo método P-Delta ficaram bastante semelhantes àqueles calculados pelo MAES, com desvios desprezíveis. O MAES, por sua vez, mostrou-se bastante trabalhoso, pois exige a modelagem de diferentes tipos de estruturas para a determinação dos esforços. / This work presents a comparative analysis of different structural systems for a 20-storey building. Each model has been designed using the principles of the direct analysis method (DAM), present in the ABNT NBR 8800:2008. The first-order amplification method (FOAM) was used to obtain, in a simplified manner, the forces acting on the building elements, including local and global second-order effects. The incidence of the wind was simulated in two different ways. In the first case, named uniform, the wind was applied without eccentricity, generating only structure overturning. In the second case, it was considered an eccentricity due to vicinity effects, prescribed by the ABNT NBR 6123:1988, responsible for causing twisting and building overturning. All numerical analysis were carried out a simplified second-order method known as P-Delta. From the results obtained it was found that the reduction of live loads in the design of columns provides material economy, but on the other hand, increases analysis time, since it requires different combinations for beams and columns. The strategy used to simulate the vicinity effects was satisfactory, because it allowed, in an easy and practical way, the consideration of the torsion produced by the wind eccentric impact. It was also observed that these effects increased the bending moments and the displacements of the structures. About the second-order effects, it was shown that, for sway or non-sway classification, the critical combination is one with greatest gravitational loading. However, for the design of the elements, it was observed that other loading conditions can be critical, especially those in which the wind is the main live load. Finally, the results obtained by the P-Delta method were very similar to those calculated by the first-order amplification method. The FOAM was, in turn, very laborious, because it requires the modeling of different types of structures for the determination of the forces.

Este trabalho apresenta uma análise comparativa de diferentes sistemas estruturais para um edifício de 20 pavimentos. Cada um dos modelos foi dimensionado através dos princípios do método da análise direta, presente na ABNT NBR 8800:2008. O método da amplificação dos esforços solicitantes (MAES) foi usado para se obter de forma simplificada os esforços atuantes nos elementos do edifício considerando os efeitos locais e globais de segunda ordem. A incidência do vento foi simulada de duas formas diferentes. Na primeira, chamada de uniforme, o vento foi aplicado sem excentricidade, gerando apenas o efeito de tombamento nas estruturas. Na segunda hipótese, considerou-se uma excentricidade devida aos efeitos de vizinhança, prescrita pela ABNT NBR 6123:1988, responsável por ocasionar o tombamento e a torção dos edifícios. Todas as análises numéricas foram repetidas fazendo o uso de outro método simplificado de segunda ordem, conhecido como P-Delta. Por meio dos resultados obtidos, constatou-se que a possibilidade de se reduzir a sobrecarga para o dimensionamento de pilares proporciona uma economia de material, mas, por outro lado, tem como consequência o aumento do tempo de análise, pois exige a utilização de diferentes combinações de cálculo para o dimensionamento de vigas e pilares. A estratégia utilizada para simular os efeitos de vizinhança mostrou-se satisfatória, pois permitiu introduzir de maneira fácil e prática a torção ocasionada pela incidência excêntrica do vento. Observou-se também que esses efeitos ocasionaram o aumento dos momentos fletores e dos deslocamentos das estruturas analisadas. Em relação à avaliação dos efeitos de segunda ordem, comprovou-se que, para a classificação da deslocabilidade, a combinação de cálculo crítica é aquela que possui o maior carregamento gravitacional. Entretanto, para o dimensionamento dos elementos, foi constatado que outras hipóteses de cálculo, principalmente aquelas em que o vento é a ação variável principal, podem ser determinantes. Por fim, foi observado que os resultados obtidos pelo método P-Delta ficaram bastante semelhantes àqueles calculados pelo MAES, com desvios desprezíveis. O MAES, por sua vez, mostrou-se bastante trabalhoso, pois exige a modelagem de diferentes tipos de estruturas para a determinação dos esforços. / This work presents a comparative analysis of different structural systems for a 20-storey building. Each model has been designed using the principles of the direct analysis method (DAM), present in the ABNT NBR 8800:2008. The first-order amplification method (FOAM) was used to obtain, in a simplified manner, the forces acting on the building elements, including local and global second-order effects. The incidence of the wind was simulated in two different ways. In the first case, named uniform, the wind was applied without eccentricity, generating only structure overturning. In the second case, it was considered an eccentricity due to vicinity effects, prescribed by the ABNT NBR 6123:1988, responsible for causing twisting and building overturning. All numerical analysis were carried out a simplified second-order method known as P-Delta. From the results obtained it was found that the reduction of live loads in the design of columns provides material economy, but on the other hand, increases analysis time, since it requires different combinations for beams and columns. The strategy used to simulate the vicinity effects was satisfactory, because it allowed, in an easy and practical way, the consideration of the torsion produced by the wind eccentric impact. It was also observed that these effects increased the bending moments and the displacements of the structures. About the second-order effects, it was shown that, for sway or non-sway classification, the critical combination is one with greatest gravitational loading. However, for the design of the elements, it was observed that other loading conditions can be critical, especially those in which the wind is the main live load. Finally, the results obtained by the P-Delta method were very similar to those calculated by the first-order amplification method. The FOAM was, in turn, very laborious, because it requires the modeling of different types of structures for the determination of the forces.