Composite Structures and Construction Systems
45 Questions
6 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the first step in the construction sequence of composite construction?

  • Pour concrete
  • Develop composite strength
  • Install deck, shear studs, and reinforcement
  • Erect steelwork (correct)

During the construction phase, why is the steel considered non-composite initially?

  • It has not yet been erected
  • It is deflecting and bending under loads (correct)
  • Concrete is not yet poured
  • Shear studs are not installed

Where is the neutral axis typically located in a composite section?

  • Near the top flange (correct)
  • At the center of the girder
  • Near the bottom flange
  • At the midpoint of the concrete slab

What is a primary consideration in the design of composite beams regarding serviceability?

<p>Addressing occupant-induced vibrations (A)</p> Signup and view all the answers

What is one of the advantages of the relatively high flexural stiffness of composite floor framing systems?

<p>Reduces perceptibility of vibrations (A)</p> Signup and view all the answers

What must be evaluated due to the increased fabrication costs associated with composite girder design?

<p>The potential savings from material efficiency (A)</p> Signup and view all the answers

What role does the deck play in the composite construction process?

<p>It stabilizes the top flange of the steel (C)</p> Signup and view all the answers

What advantage do composite girders offer in terms of building services?

<p>Accommodates mechanical ducts and related services (A)</p> Signup and view all the answers

What are the component frequencies used to evaluate the fundamental frequency of the floor system?

<p>fc1, fc2, and fc3 (D)</p> Signup and view all the answers

Which mode shapes are considered in the design of the secondary and primary beam?

<p>Girder mode and joist mode (C)</p> Signup and view all the answers

Which assumption is made about the floor's vibration response in current design guidance?

<p>It only considers the first mode of vibration. (D)</p> Signup and view all the answers

What is the significance of the two-mode shapes in determining the floor's fundamental frequency?

<p>They help identify the lowest frequency value. (C)</p> Signup and view all the answers

What is the relationship between the identified component frequencies and the boundary conditions?

<p>Component frequencies vary based on their boundary conditions. (A)</p> Signup and view all the answers

What is one economic advantage of fabricated tapered beams?

<p>They can be designed for specific moment and shear resistance. (D)</p> Signup and view all the answers

What design consideration is common for simply supported tapered beams?

<p>Tapering to a minimum depth at both ends. (A)</p> Signup and view all the answers

What role do web stiffeners play in tapered beam design?

<p>They enhance the shear resistance of the web. (C)</p> Signup and view all the answers

What is one feature of haunched beams that differentiates them from other types?

<p>They offer rigid moment connections between beams and columns. (A)</p> Signup and view all the answers

How can haunched beam design contribute to economy in construction?

<p>It can lead to a reduction in beam depth by up to 30%. (B)</p> Signup and view all the answers

What happens to the critical section of a haunched beam when designed for a moment larger than its plastic moment resistance?

<p>It shifts to the tip of the haunch. (A)</p> Signup and view all the answers

In what ways can the space created by tapered web beams be utilized?

<p>For running services of modest size. (D)</p> Signup and view all the answers

What is the maximum recommended span for tapered beams to maintain economic efficiency?

<p>Up to 20 m. (B)</p> Signup and view all the answers

What is the typical length of a haunch for non-sway frames as a percentage of the span length?

<p>5 to 7% (B)</p> Signup and view all the answers

Why are haunched composite beams typically used?

<p>When the beams frame directly into the major axis of the columns (A)</p> Signup and view all the answers

What is one of the main advantages of haunched beams during the steel erection stage?

<p>Higher strength and stiffness (A)</p> Signup and view all the answers

What is required of columns when using haunched connections?

<p>They must be designed to resist the moment transferred from the beam (C)</p> Signup and view all the answers

How do haunched connections behave under different moments?

<p>They behave differently under positive and negative moments (A)</p> Signup and view all the answers

What is a benefit of using a parallel beam system?

<p>Avoidance of cutting secondary beams at junctions (B)</p> Signup and view all the answers

What is the expected advantage of continuous construction with primary beams?

<p>Reduced overall steel weight (C)</p> Signup and view all the answers

What type of loads can rigid frame action from haunched connections resist?

<p>Lateral loads due to wind (C)</p> Signup and view all the answers

What was identified as a significant issue in early composite structures involving steel and concrete?

<p>Longitudinal slip between elements (C)</p> Signup and view all the answers

Which components are typically involved in a composite floor system?

<p>Steel beams, concrete slab, and shear connectors (A)</p> Signup and view all the answers

What is a primary advantage of using a composite construction system?

<p>Reduced foundation costs (B)</p> Signup and view all the answers

How much lighter are composite systems compared to traditional concrete construction?

<p>20 to 40% (B)</p> Signup and view all the answers

What type of loads do composite floor systems primarily resist?

<p>Gravity loads (B)</p> Signup and view all the answers

What were composite steel-concrete beams identified as?

<p>The earliest form of composite construction (D)</p> Signup and view all the answers

What allows for a reduction in construction time with composite systems?

<p>The ability to cast additional floors without waiting for lower floors to gain strength (C)</p> Signup and view all the answers

Which of the following does not represent a benefit of composite systems?

<p>Longer construction duration (A)</p> Signup and view all the answers

What is a major concern when designing beams longer than 12 meters?

<p>They need a larger required flexural stiffness. (C)</p> Signup and view all the answers

What is the main advantage of using castellated composite beams?

<p>Reduction of deflection and vibration problems. (C)</p> Signup and view all the answers

In which zone is the best location for a web opening in beams?

<p>Low shear zone. (A)</p> Signup and view all the answers

What limitation is associated with castellated beams regarding mechanical services?

<p>Standard castellated openings may be too small. (C)</p> Signup and view all the answers

What effect does the incorporation of mechanical services have on long-span beam design?

<p>It requires modification of serviceability design. (B)</p> Signup and view all the answers

What is a potential drawback of using castellated beams?

<p>They are expensive to fabricate. (D)</p> Signup and view all the answers

What is indicated about the height and length of web openings in beams?

<p>The height should not be more than 70% of the beam depth. (A)</p> Signup and view all the answers

Which structural aspect is less contributed to by the webs of beams?

<p>Shear resistance. (A)</p> Signup and view all the answers

Flashcards

Composite construction

A construction method combining steel and concrete to create stronger and lighter structures.

Composite steel-concrete beams

The earliest type of composite construction, using steel and concrete in flexural members.

Shear connectors

Components used to prevent longitudinal slip between steel and concrete in composite structures.

Composite floor systems

Floor systems using steel beams/joists, and concrete slabs to create a T-beam structure.

Signup and view all the flashcards

T-beam flexural member

A structural member combining the strength of a steel beam and a concrete slab.

Signup and view all the flashcards

Advantages of composite construction

Improved strength, lighter weight, faster construction, and lower costs.

Signup and view all the flashcards

Longitudinal slip

The unwanted movement or separation between steel and concrete components in composite structures, a problem originally needing addressing in early composite designs.

Signup and view all the flashcards

Weight reduction in composite construction

Composite structures are typically 20-40% lighter than all-concrete structures, reducing foundation and material costs.

Signup and view all the flashcards

Long-span beams

Steel beams longer than 12 meters, requiring special design considerations due to increased deflection and vibration.

Signup and view all the flashcards

Serviceability design

Ensuring a beam functions properly under normal use, avoiding excess deflection and vibrations that disturb occupants.

Signup and view all the flashcards

Castellated beams

Steel beams with zigzag cutouts in the web, creating open spaces that reduce weight and allow for passing mechanical services.

Signup and view all the flashcards

Composite action

The interaction between steel and concrete in a composite beam, increasing stiffness without significantly increasing strength.

Signup and view all the flashcards

Shear capacity

The ability of a beam to resist forces that try to cut it across its width.

Signup and view all the flashcards

Horizontal stiffeners

Reinforcements that strengthen the web openings in castellated beams, preventing excessive bending or buckling.

Signup and view all the flashcards

Low shear zone

Area in a beam where shear forces are minimal, making it ideal for placing open sections or openings.

Signup and view all the flashcards

Moment resistance

A beam's ability to resist bending forces that cause it to deflect or deform.

Signup and view all the flashcards

Composite construction sequence

The steps involved in building a composite structure, starting with steel erection, followed by deck & reinforcement installation, and finally concrete pouring.

Signup and view all the flashcards

Composite beam: early stages

After concrete pouring, the steel beam is initially non-composite, meaning it bends due to the weight of wet concrete and construction loads. The deck provides stability to the top flange during this stage.

Signup and view all the flashcards

Composite beam: final state

As concrete sets, the beam gains composite strength, meaning it becomes a strong unit of steel and concrete working together, capable of supporting all future loads.

Signup and view all the flashcards

Composite floor plan

A building floor plan that utilizes composite steel beams, often seen as a typical design for efficient and sturdy floors.

Signup and view all the flashcards

Stress distribution in a composite beam

The stress mainly concentrates on the top flange of the steel section, while the bottom flange is lightly stressed. This allows for wider steel flanges for shear stud and deck installation, but requires considering the increased fabrication cost.

Signup and view all the flashcards

Composite girder with openings

Composite girders can be designed with openings to allow the passage of mechanical ducts and services through the depth of the girder, making installation easier and more flexible.

Signup and view all the flashcards

Serviceability issues in composite beam design

Design considerations include long-term deflections (creep) and floor vibrations, especially occupant-induced vibrations. Composite floors often have high stiffness, resulting in lower vibration amplitudes and reduced noise.

Signup and view all the flashcards

Haunched Beam

A beam with a thickened section at the ends, increasing its moment capacity and stiffness.

Signup and view all the flashcards

Haunch Depth

The vertical thickness of the thickened section of a haunched beam. It's determined by the required bending moment at the beam-column connection.

Signup and view all the flashcards

Haunch Length

The horizontal distance of the thickened section of a haunched beam.

Signup and view all the flashcards

Sway Frame

A structural frame prone to lateral movement (sideways movement) under wind or seismic loads

Signup and view all the flashcards

Non-Sway Frame

A structural frame that is stiff and resists lateral movement without significant deformation.

Signup and view all the flashcards

Parallel Beam System

A system with two main beams running parallel, supporting secondary beams running over them. This reduces construction depth and allows for large service ducts.

Signup and view all the flashcards

Secondary Beams in Parallel Beam System

Smaller beams running over the main beams in a parallel beam system, designed to act compositely with the slab.

Signup and view all the flashcards

Continuous Construction

A method of building where beams are extended over multiple spans without full breaks, reducing steel weight and complexity.

Signup and view all the flashcards

Dunkerly's Approximation

A method to estimate the fundamental frequency of a composite floor system by combining the individual frequencies of its components (slab, beams, etc.).

Signup and view all the flashcards

Component Frequencies

The individual frequencies of the different parts of a composite floor system, such as the slab, secondary beams, and primary beams.

Signup and view all the flashcards

Fundamental Frequency

The lowest natural vibration frequency of a floor system, indicating the most likely frequency it will vibrate at during use.

Signup and view all the flashcards

Two-mode Shapes

Two distinct ways a floor system can deform or vibrate when subjected to load: one for the secondary beams (joists) and another for the primary beams (girders).

Signup and view all the flashcards

Fabricated Tapered Beams

Beams designed with varying depths along their length to optimize strength and efficiency based on load distribution. This design allows for thinner sections at the ends where the bending moment is lower and thicker sections in the middle where the bending moment is higher.

Signup and view all the flashcards

Tapered Beam Advantage

Fabricated tapered beams offer economic benefits by using less material where it's not needed, reducing overall cost. This design also allows for efficient use of space within the beam for services and utilities.

Signup and view all the flashcards

Hybrid Girder

A type of fabricated beam that combines different grades of steel in its components. Typically, a stronger steel is used for the bottom flange while a less strong steel is used for the top flange.

Signup and view all the flashcards

Stiffeners in Tapered Beams

These are added to the web of a tapered beam to increase its shear resistance, particularly when the web is too thin or the slope of the taper is too steep.

Signup and view all the flashcards

Haunch Connection

The rigid connection between a haunched beam and a column, which helps to reduce mid-span deflection and bending moments by transferring load efficiently.

Signup and view all the flashcards

Haunched Beams and Continuous Design

These beams often benefit from continuous design principles, which can lead to significant cost savings by further reducing the required depth of the beam.

Signup and view all the flashcards

Critical Section in Haunched Beams

The location where the bending moment reaches its maximum value and the risk of failure is highest. In haunched beams, this section is often located at the tip of the haunch.

Signup and view all the flashcards

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.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Composite Structures CIVIL3811/9811 PDF

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.

More Like This

Composite Structures Maintenance Task Quiz
3 questions

Composite Structures Maintenance Task Quiz

DaringDream avatar
DaringDream
Week 1: Composite Structures Strength
40 questions

Week 1: Composite Structures Strength

SweetheartMandelbrot1035 avatar
SweetheartMandelbrot1035
Composite Structures and Vibration Control
9 questions

Composite Structures and Vibration Control

SweetheartMandelbrot1035 avatar
SweetheartMandelbrot1035
Composite Structures & Prestressed Concrete
45 questions

Composite Structures & Prestressed Concrete

SweetheartMandelbrot1035 avatar
SweetheartMandelbrot1035
Use Quizgecko on...
Browser
Open
Browser
Browser