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What is the first step in the construction sequence of composite construction?
What is the first step in the construction sequence of composite construction?
During the construction phase, why is the steel considered non-composite initially?
During the construction phase, why is the steel considered non-composite initially?
Where is the neutral axis typically located in a composite section?
Where is the neutral axis typically located in a composite section?
What is a primary consideration in the design of composite beams regarding serviceability?
What is a primary consideration in the design of composite beams regarding serviceability?
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What is one of the advantages of the relatively high flexural stiffness of composite floor framing systems?
What is one of the advantages of the relatively high flexural stiffness of composite floor framing systems?
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What must be evaluated due to the increased fabrication costs associated with composite girder design?
What must be evaluated due to the increased fabrication costs associated with composite girder design?
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What role does the deck play in the composite construction process?
What role does the deck play in the composite construction process?
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What advantage do composite girders offer in terms of building services?
What advantage do composite girders offer in terms of building services?
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What are the component frequencies used to evaluate the fundamental frequency of the floor system?
What are the component frequencies used to evaluate the fundamental frequency of the floor system?
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Which mode shapes are considered in the design of the secondary and primary beam?
Which mode shapes are considered in the design of the secondary and primary beam?
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Which assumption is made about the floor's vibration response in current design guidance?
Which assumption is made about the floor's vibration response in current design guidance?
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What is the significance of the two-mode shapes in determining the floor's fundamental frequency?
What is the significance of the two-mode shapes in determining the floor's fundamental frequency?
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What is the relationship between the identified component frequencies and the boundary conditions?
What is the relationship between the identified component frequencies and the boundary conditions?
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What is one economic advantage of fabricated tapered beams?
What is one economic advantage of fabricated tapered beams?
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What design consideration is common for simply supported tapered beams?
What design consideration is common for simply supported tapered beams?
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What role do web stiffeners play in tapered beam design?
What role do web stiffeners play in tapered beam design?
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What is one feature of haunched beams that differentiates them from other types?
What is one feature of haunched beams that differentiates them from other types?
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How can haunched beam design contribute to economy in construction?
How can haunched beam design contribute to economy in construction?
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What happens to the critical section of a haunched beam when designed for a moment larger than its plastic moment resistance?
What happens to the critical section of a haunched beam when designed for a moment larger than its plastic moment resistance?
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In what ways can the space created by tapered web beams be utilized?
In what ways can the space created by tapered web beams be utilized?
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What is the maximum recommended span for tapered beams to maintain economic efficiency?
What is the maximum recommended span for tapered beams to maintain economic efficiency?
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What is the typical length of a haunch for non-sway frames as a percentage of the span length?
What is the typical length of a haunch for non-sway frames as a percentage of the span length?
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Why are haunched composite beams typically used?
Why are haunched composite beams typically used?
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What is one of the main advantages of haunched beams during the steel erection stage?
What is one of the main advantages of haunched beams during the steel erection stage?
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What is required of columns when using haunched connections?
What is required of columns when using haunched connections?
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How do haunched connections behave under different moments?
How do haunched connections behave under different moments?
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What is a benefit of using a parallel beam system?
What is a benefit of using a parallel beam system?
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What is the expected advantage of continuous construction with primary beams?
What is the expected advantage of continuous construction with primary beams?
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What type of loads can rigid frame action from haunched connections resist?
What type of loads can rigid frame action from haunched connections resist?
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What was identified as a significant issue in early composite structures involving steel and concrete?
What was identified as a significant issue in early composite structures involving steel and concrete?
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Which components are typically involved in a composite floor system?
Which components are typically involved in a composite floor system?
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What is a primary advantage of using a composite construction system?
What is a primary advantage of using a composite construction system?
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How much lighter are composite systems compared to traditional concrete construction?
How much lighter are composite systems compared to traditional concrete construction?
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What type of loads do composite floor systems primarily resist?
What type of loads do composite floor systems primarily resist?
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What were composite steel-concrete beams identified as?
What were composite steel-concrete beams identified as?
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What allows for a reduction in construction time with composite systems?
What allows for a reduction in construction time with composite systems?
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Which of the following does not represent a benefit of composite systems?
Which of the following does not represent a benefit of composite systems?
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What is a major concern when designing beams longer than 12 meters?
What is a major concern when designing beams longer than 12 meters?
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What is the main advantage of using castellated composite beams?
What is the main advantage of using castellated composite beams?
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In which zone is the best location for a web opening in beams?
In which zone is the best location for a web opening in beams?
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What limitation is associated with castellated beams regarding mechanical services?
What limitation is associated with castellated beams regarding mechanical services?
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What effect does the incorporation of mechanical services have on long-span beam design?
What effect does the incorporation of mechanical services have on long-span beam design?
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What is a potential drawback of using castellated beams?
What is a potential drawback of using castellated beams?
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What is indicated about the height and length of web openings in beams?
What is indicated about the height and length of web openings in beams?
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Which structural aspect is less contributed to by the webs of beams?
Which structural aspect is less contributed to by the webs of beams?
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Study Notes
Composite Structures
- Composite construction, as currently understood, utilizes steel and concrete for flexural members. The initial forms of composite structures appeared over a century ago in the U.S.
- Early composite steel-concrete beams had the issue of longitudinal slip between the steel and concrete components.
- An American engineer developed a patent for shear connectors to prevent longitudinal slip at the top flange of universal steel sections. This marked the beginning of fully composite steel-concrete systems.
Composite Construction Systems for Buildings
- Composite floor systems usually involve steel beams, joists, girders, or trusses and a concrete floor slab that create a T-beam flexural member.
- The system's strength arises from the concrete's compression strength and the steel's tensile strength.
- Core advantages: steel and concrete combine for ideal strength, composite construction is about 20-40% lighter than concrete-only construction (simplifying site erection and installation), and potentially reduced foundation costs.
Composite Construction Time Systems for Buildings
- Construction time is reduced by casting additional floors without waiting for prior floors to gain necessary strength. Positive moment reinforcement from the steel deck helps control cracking and provides fire resistance.
- Labor requirements are lower with composite floors; steel decking acts as permanent formwork. Composite beams/slabs accommodate raceways for electrical, communication, and air systems; the slab can also serve as ceiling.
- The composite slab's in-plane diaphragm capability enables effective lateral bracing for beams.
- Concrete provides ongoing corrosion and thermal protection for the steel at elevated temperatures. Composite slabs can achieve a two-hour fire rating.
The Floor Slab Construction Methods
- Four main methods for constructing composite floor slabs: flat-soffit reinforced concrete, precast concrete planks with cast-in-situ topping, precast concrete slabs with in-situ grouting, and a metal steel deck with concrete (either composite or non-composite).
- Composite action in metal decks occurs due to side embossments built into the steel sheet profile. The result is a rigid horizontal diaphragm that provides stability, while distributing wind and seismic loads to the lateral load-resisting systems.
Construction Sequence of the Composite Construction
- Erect steelwork, install deck, shear studs, and reinforcement, then pour concrete.
- Initial stage of composite construction (before concrete sets): steel structure acts as a non-composite member, deflecting under wet concrete and construction loads. The deck stabilizes the top flange.
- Concrete sets; the beam gains composite strength and supports added loads.
Composite Construction Systems for Buildings - Additional Aspects
- For long-span composite floors, design elements must consider the effects of vibrations (both human and mechanical).
- The type of floor beam (castellated, haunched, parallel) impacts how easily it carries mechanical/electrical systems passing through the structure, and also determines serviceability requirements/efficiency.
Composite Columns
- Steel-encased composite columns have been used for over 100 years. The use of composites in columns began with fire rating considerations, but evolved to include strength and stability improvements.
- Main benefit: ability to achieve higher steel percentages than conventional RC structures. Steel erection columns accelerate construction, and the steel provides excellent load-bearing functionality before concrete placement.
- During construction, concrete encasing acts as permanent formwork.
Composite Connections
- Connections in composite beams and columns can have different design strategies based on the presence/absence of live load in conjunction with the concrete topping.
- Design calculations must account for the moment-resisting capacity of these connections. Various connection designs are discussed (flush end plates bolted to the column flange, bottom angles, etc).
Vibration characteristics of steel-concrete composite floor systems
- Trends in long-span, lightweight steel-concrete floors have lead to consideration of vibration problems, usually induced by human/mechanical activities within/on the structure.
- Design should account for the frequency and intensity of vibrations.
Natural Frequency
- For free elastic vibration, the natural frequency is defined by Equation 1; values for different boundary conditions are provided in the text for use in analysis.
- A method for estimating the natural frequency of composite floors is described, using Equation 3 and the component frequencies/deflections.
References
- This section lists publications on Vibration characteristics of steel-concrete composite floor systems and Composite steel-concrete structures for use in further research.
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Description
Explore the development and application of composite structures that combine steel and concrete. This quiz covers the historical evolution of composite beam technology, including shear connectors that prevent slippage. Learn about the advantages of composite floor systems in modern construction and their efficient material use.
