Location of Construction Joint

Following points are helpful to provide construction joint in RC Slab, Beam and Raft Foundation:

  1. Construction joint shall be provided preferably at a location where stress are zero.
  2. Construction joint is provided at one-third or end of support.
  3. Also provide key and rebar to transfer shear stress if shear stress is not zero at point of construction joint.
  4. Provide construction joints as minimum as possible.
  5. Construction joint shall not be left on discretion of contractor. It must be approved by designer.

Definition:

Construction joints are placed at the end of a day’s work. In slabs, they may be designed to permit movement and/or to transfer load. Often in reinforced concrete a conscious effort is made to clean the joint and bond the next day’s work.[1].

Explanation:

The number of construction joints in concrete structures should be minimized. If construction joints are necessary to facilitate construction, it is normally aligned perpendicular to the direction of the member. For beams and slabs, construction joints are preferably located at about one-third of the span length. The choice of this location is based on the consideration of low bending moment anticipated with relatively low shear force. However, location of one-third span is not applicable to simply supported beams and slabs because this location is expected to have considerable shear forces and bending moment when subjected to design loads. Sometimes, engineers may tend to select the end supports as locations for construction joints just to simplify construction. [2].

Construction joint is not preferred at midspan. When formwork removed from construction pours (delay in next pouring) and the beam (or slab) has had to cantilever from the previous support to the new construction joint. Also, joints at midspan do not typically work for post-tensioned construction. you need to accommodate anchorages and at approx 1/3 span works best. [3].

You need to provide a joint with key and rebars crossing the joint. In raft footing, at construction joint, shear force may not be minimum/zero. Hence you will have to leave dowels from one pour to another pour to transfer shear. You may calculate area of reinforcement required based on permissible shear stress as 0.45 fy. [4].

You can have your opinion and suggestion in comment box below.

Reference:

  1. CADMAN
  2. A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
  3. eng-tips
  4. sefindia.org

Additional Reference:

  1. ACI 302.1, “Guide for Concrete Floor and Slab Construction,” ACI Manual of Concrete Practice.
  2. “Slabs on Grade,” ACI Concrete Craftsman Series, American Concrete Institute, Detroit, Mi.
  3. “Cracks in Concrete: Causes, Prevention, Repair,” a collection of articles from Concrete Construction Magazine, June, 1973.

Lectures on Advanced Structural Analysis I

Following are course content on Advanced Structural Analysis I

Course Intructor: Prof. Dr. Shahzad Rahman

Course Outline

Lectures

Lecture 1: Overview of Bernoulli-Euler Beam Theory, Theory of Torsion, Static Indeterminancy, Kinematic Indeterminancy

Lecture 2: Slope-Deflection Method

Lecture 3: Virtual Work Principles

Lecture 4: Moment Distribution Method

Lecture 5: Modifications in Moment Distribution Method

Lecture 6: Moment Distribution Method – Frame with Side Sway

Lecture 7: Compatibility Method of Analysis

Lecture 8: Matrix Analysis of Structures

Lecture 9: Matrix Analysis / Stiffness Method

Lecture 10: Matrix Analysis / Stiffness Method Contd.

Lecture 11: Matrix Analysis / Stiffness Method – Static Condensation

Lecture 12: Approximate Analysis

Lecture 13: Matrix Analysis – Member Releases

Labs

Introduction to SAP2000

Assignments

Assignment 1: Slope and Deflection of Beam

Assignment 2: Displacements in Truss

Assignment 3: Solving Beam using Moment Distribution Method

Solution of Assignments

Exam

Mid Term Exam Paper

Solution of Mid Term Paper

Final Term Exam Paper and Solution