Structural Engineering: Brackets and Corbels

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Questions and Answers

What is the value of the total shear friction steel (Avf)?

644 mm²

1116 mm² (correct)

1055 mm²

626 mm²

How is the nominal tensile strength area (An) determined?

By calculating $\dfrac{N_{uc}}{∅f_y}$ (correct)

By using the formula for steel area at a certain depth

Using shear strength equations

By taking the average of two areas

What is the value of the bending moment (Mu) calculated in the given content?

625 KN.m

71 KN.m (correct)

98 KN.m

492 KN.m

When determining the shear area (Asc), what is the minimum requirement?

Asc must be greater than or equal to $\dfrac{A_{uf}+A_n}{2}$ Signup and view all the answers

What is the final area of the top bracket rebar (Asc) after checking requirements?

1055 mm² Signup and view all the answers

What is the primary purpose of brackets in structural engineering?

To support concentrated loads from beams or slabs. Signup and view all the answers

Which type of failure is characterized by poor detailing of the embedded length?

Type 1 Shear Failure Signup and view all the answers

What governs the design of brackets and corbels according to their behavior?

Shear forces Signup and view all the answers

What is a Strut-and-tie model (STM) used for in the context of brackets and corbels?

To better capture load transfer mechanisms. Signup and view all the answers

What issue may arise from having a small thickness of a corbel?

Type 2 Shear Failure Signup and view all the answers

In the design of brackets, what role do the top bars at the column face play?

They transfer bending moments to vertical members. Signup and view all the answers

What must be carefully considered to avoid shear failure in brackets?

Amount of stirrups provided. Signup and view all the answers

Why is horizontal tension reinforcement necessary in brackets and corbels?

To resist horizontal forces from bending moments. Signup and view all the answers

What is the maximum allowed span ratio for using the flexural model in bracket design?

av/d ≤ 1 Signup and view all the answers

Which equation represents the nominal shear strength for normal weight concrete?

$V_n = rac{0.2 fc bd}{(3.3+0.08 fc) bd}$ Signup and view all the answers

Under what condition must a horizontal tensile force be assumed in bracket design?

Nue ≥ 0.2 Vu Signup and view all the answers

What is the appropriate equation to calculate the area of steel required to resist moment Mu?

$A_f = rac{Mu}{φf_y(d-a/2)}$ Signup and view all the answers

Which of the following is NOT a condition for determining the total area required for flexure and direct tension at the top of the bracket?

$A_sc = A_f + A_n - A_{vf}$ Signup and view all the answers

What is the minimum area of closed hoop stirrups required in relation to the area of the tensile reinforcement?

$A_h ≥ 0.5(A_sc - A_n)$ Signup and view all the answers

What is the recommended friction factor (μ) for normal weight concrete?

1.4 Signup and view all the answers

Which material strengths are cited for the example in designing the bracket?

f'c = 35 MPa and f''y = 420 MPa Signup and view all the answers

Study Notes

Introduction

Brackets and corbels are short cantilever beams
They project from columns or walls
Support loads like beams or slabs
Structural behavior differs from conventional beams
Short span, large applied forces (high shear stresses)
Deep section relative to their length
ACI 318 code provides design guidelines

Brackets

Short cantilevers used to support concentrated loads
Usually project from columns or walls

Corbels

Short cantilevers extending from columns or walls
Typically deeper in section
Transfer loads from horizontal members (beams) to vertical members (columns)

Failure Modes

Causes of failure include:
- Small amount of main steel
- Low compressive strength with high main steel
- Small amount of reinforcement crossing the strut
- Small amount of stirrups
- Loss of anchorage
- Lack in the detailing of embedded length
- Small thickness of corbel
- High value of horizontal load
- Lack in the seat plate detailing

Behavior of Brackets and Corbels

Experience high shear forces and moments
Shear-controlled design (shear force often governs the design)
Strut-and-tie models (STM) used for analysis and design to capture load transfer mechanisms
Horizontal tension reinforcement needed to resist horizontal forces
Provide additional capacity for crack control

Design Considerations

Bracket considered as a short cantilever with flexural tension at column face
Strut and tie model for performance analysis
Span ratio (av/d) ≤ 1 and (a/d) ≤ 2 determine design method (flexural/strut and tie)
Depth at the outside edge of bearing area (t ≥ 0.5d)
Mu ≤ ØMn and Vu ≤ ØVn with Ø=0.75
Horizontal tensile force must be considered without roller/low-friction support pad
Find d according to specified formulas

Additional Calculations

Calculations involve finding the amount of steel (A) required to resist moment (Mu), area of steel (An) for nominal tensile strength and shear-friction reinforcement (Av)
Total area required for flexure and direct tension
Closed hoop stirrups (Ah) area should be greater than 0.5(Asc - An), 0.5 Af, and Avf / 3
Example calculations for column bracket with end reaction and vertical load specifications for specific material strengths.

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Description

Explore the structural principles behind brackets and corbels, and their unique functions as short cantilever beams. This quiz covers design guidelines, failure modes, and key characteristics as outlined in ACI 318. Gain a deeper understanding of how these elements support loads in construction.