CE421 REINFORCED CONCRETE

STRUCTURE DESIGN

INTRODUCTION

IntroductionArchitectural Project:

• shows layout plan (position of the structure within the land area)

• storey plans

• vertical sections, etc.

It includes the dimensions of the different structural

parts, walls, positions of the doors, windows,

isolation coating, etc. But not the columns! The locations

of the columns should be decided by both engineer and

architect; but its under the responsibility of engineer!

Introduction1. Data Collection:

• Architectural project is obtained,

• the construction site is investigated,

• information about the soil type is obtained (soil survey),

• information required for the determination of earthquake, wind and snow loads are gathered,

• types of the structural system and materials are determined.

2. Selection of the roof type and determination of the roof loads.

3. Preliminary design for the slabs (selection of thickness) and determination of the slab loads («G» or «Q»/m2).

4. Design of the slabs (reinforcement).

5. Design of the staircase.

6. Estimation of the beam and column loads, and their preliminary design (selection of beam/column dimensions).

7. Modeling of the structure (3D computer aided) and modal analysis.

8. Determination of the natural periods (Tn) from modal analysis.

Introduction9. Calculation of environmental (earthquake, wind and snow) loads.

10. Assignment of all loads in the 3D model and structural analysis.

11. Beam design (longitudinal «flexural» and transverse «shear» reinforcement).

12. Column design (longitudinal «axial+flexural» and transverse «shear» reinforcement).

13. Design of shear walls.

14. Shear check for the beam-column connections.

15. Design of foundations.

16. Check for the Earthquake Code (lateral drift ratio, strong column-weak beam, etc.).

17. Preparation of the formwork plan and design drawings.

IntroductionFormwork Plan: includes positions and dimensions of the structural members(slabs, beams, columns, shear walls, etc.). It is prepared at 1/50 scale. The axes andID’s of the members are also mentioned on the plan. It illustrates a plan view of thestructural load carrying system.

IntroductionBeam Design Drawings: They are prepared at 1/20 scale and show thelongitudinal/transverse reinforcement of the beams. The diameters, numbers,spacing, length and lapped length of the reinforcements are plotted seperately foreach beam.

Beam Reinforcements Drawings

IntroductionColumn/Shear Wall Design Drawings: The column application plan is preparedat 1/50 scale and columns/shear walls are illustrated at 1/20 scale on this plan. Thelongitudinal/transverse reinforcement details are given on these drawings.

IntroductionWhile choosing the structural system:

• slabs should be supported by the beams,

• beams should be continuous and supported by columns/shear walls at its bothends,

• columns should transfer its force to another column (not end on a beam or slab),

• columns (beams) in one direction should be parallel to each other,

• there should be enough number of shear walls to resist lateral (earthquake) forces,

• structural system (especially columns/shear walls) should be positioned assymmetric as possible.

IntroductionThere are two main duties of the beams:

I. Transfer the distributed loads from the slabs to the colums.

II. Distribute the lateral (earthquake/wind) forces in between the columns/shearwalls.

Where do we place «beams»:

1. Under each partition (infill) wall, we place a beam.

IntroductionWhere do we place «beams»:

2. If the span of the slab in between these beams decided in the 1st stage exceed 5 m.,additional (secondary) beams are placed to decrease this span length.

3. The distribution of the beams decided in the 1st stage may be too close to each other(closer than 1 m.). In that case, the number of beams may be decreased. Only thebeams under the interior infill walls (with a less thickness) may be removed. In thatcase, the distributed load of the interior infill walls are applied on the slab (at least 1.5kN/m2).

IntroductionThere are two main duties of the columns:

I. Transfer the vertical loads from the beams to the foundation.

II. Resist the lateral loads resulted by earthquake or wind.

Where do we place «columns»:

1. At each point where beams intersect (by not disturbing the architectural use ofthe spacings).

2. If the span of beam is more than 6 m., columns may be placed in between todecrease the beam span length.

3. In rare cases, if the columns are very close, one of the columns may be removedor two columns may be combined. In that case there will be beams carried byother beams (not columns). It is not something desired!

4. Columns are placed so as to provide almost equal shear resistance in bothdirections.

IntroductionThere is one main duty of the shear walls: that is to resist lateral shear(earthquake/wind) forces and decrease the lateral drift of the structure.

Where do we place «shear walls»:

1. Shear walls are placed at the outer circumference of the structure symmetricallyalong both x and y directions (as far as possible).

2. The areas of the shear walls along both x and y directions should satisfy:

𝐴𝑠ℎ𝑒𝑎𝑟 𝑤𝑎𝑙𝑙 ≥ 0.0015 × 𝑛 × 𝐴𝑝𝑙𝑎𝑛 and 𝐴𝑠ℎ𝑒𝑎𝑟 𝑤𝑎𝑙𝑙

𝐴𝑝𝑙𝑎𝑛≥ 0.008

Ashear wall: Cross-sectional area of the shear walls along the x or y direction.

Aplan: Whole plan area of the floor

n: number of stories.

Introduction𝐴𝑝𝑙𝑎𝑛 = 7.5 × 14 = 105 𝑚2

𝐴𝑠ℎ𝑒𝑎𝑟 𝑤𝑎𝑙𝑙,𝑥 = 2 × 0.25 × 2 = 1.0 𝑚2

𝐴𝑠ℎ𝑒𝑎𝑟 𝑤𝑎𝑙𝑙,𝑦 = 2 × 0.25 × 3.5 = 1.75 𝑚2

𝐴𝑠ℎ𝑒𝑎𝑟 𝑤𝑎𝑙𝑙 ≥ 0.0015 × 𝑛 × 𝐴𝑝𝑙𝑎𝑛 and 𝐴𝑠ℎ𝑒𝑎𝑟 𝑤𝑎𝑙𝑙

𝐴𝑝𝑙𝑎𝑛 ≥ 0.008

Along x-direction:

1.0 𝑚2 ≥ 0.0015 × 6 × 105 = 0.945𝑚2 and 1.0105 = 0.0095 ≥ 0.008

Along y-direction:

1.75 𝑚2 ≥ 0.0015 × 6 × 105 = 0.945𝑚2 and 1.75105 = 0.0167 ≥ 0.008

Introduction

Case I Case II

As the symmetry in placing the shear walls both along x and y directions diminishes, the mass center (generally close to the

geometrical center) and shear center gets away from each other. This causes a torsional moment about z-axis in plan (A1

irregularity in TEC). This torsional moment increases shear force of the columns/shear walls (especially those at the outer

circumference). Therefore, shear walls should generally be placed at the outer circumference of the structure and as

symmetrical as possible both along x and y directions.

IntroductionWhat should you recall from previous lectures (CE307 Reinforced Concrete)?

All content of CE307 Reinforced Concrete is essential for success in this course.

But you should especially recall preliminary and final design of beams and columns

(determination of dimensions, flexural and shear reinforcement).

Reading Assignment:

• Reinforced Concrete Mechanics and Design, MacGregor and Wight, Chapter 2.

• Lecture Notes-Ahmet Topçu, Betonarme_2_2 (particularly Pages 26-40).

• Betonarme Yapıların Hesap ve Tasarımı, Adem Doğangün, Chapter 4.