Construction Joints – The surface of all construction joints must be cleaned, and all laitance must be removed. Before new concrete can be placed, all construction joints must be wetted, and all standing water shall be removed. The strength of a structure must not be impaired by construction joints.
- All construction joints should be located within the middle third of spans of slabs, beams, and girders.
- Vertical support members that are still plastic must not be used to support beams, girders, or slabs.
- Except when shown otherwise in design drawings or specifications, beams, girders, haunches, drop panels, and capitals are to be placed monolithically as part of a slab system.
Reinforcements that are partially embedded in concrete are not allowed to be bent in the field. The only exception to this is if the bending is shown on design drawings or is permitted by an engineer. Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9781856175494000149
- 1 How many types of joints are there in a concrete structure?
- 2 Why do we need construction joints for beam construction?
- 3 What are the four types of structural joints?
- 4 What are the different types of concrete joints?
What is a construction joint?
What is a Construction Joint? A construction joint is a type of concrete joint that is used when a new section of concrete is poured adjacent to another concrete section that has already set. The purpose of a construction joint is to allow for some horizontal movement, while being rigid against rotational and vertical movement.
- Construction joints prevent the premature failure of the concrete structure.
- A construction joint is used when a concrete slab that has already set must be joined with a new section of concrete.
- There are several reasons why this may be necessary.
- One is that construction work must pause at some point (e.g., the end of the day), thus one concrete section is inevitably allowed to set before subsequent sets.
When work resumes it is desirable for the new section and the old section to act as similar to one large slab as possible. Construction joints can have several different geometries, including straight wall butt joints and tongue and groove joints. An alternative method to join a concrete slab that is already set with another concrete slab is to place a tie bar through each, thus connecting them together. : What is a Construction Joint?
Where can construction joints be placed on a slab?
Location Selection of Construction Joint – The selection of location of a construction joints is important for the durability and effectiveness load transfer. The following are the points to be remembered while locating the joints,
Construction joints parallel to the slab span can be placed anywhere, except those locations in T-beam construction that rely on a portion of the slab to act with the beam in resisting flexure. For slabs and beams it is, therefore, usual to have construction joints at mid span of the middle third of the span. (ACI 318-11, Section 6.4.4). Joints in girders shall be offset a minimum distance of two times the width of intersecting beams. (ACI 318-11, Section 6.4.5). Designing concrete members for lateral forces may require special design treatment of construction joints. In walls a horizontal length of placement in excess of 40 ft is not normally recommended. It is convenient to locate horizontal joints at the floor line or in line with window sills. In the design of hydraulic structures, construction joints usually are spaced at shorter intervals than in non hydraulic structures to reduce shrinkage and temperature stresses. If the placing of concrete is involuntarily stopped for a time longer than the initial setting time of the concrete, the old surface is to be considered as a construction joint, and treated as such before casting is resumed. However from the point of view of strength of the structure, it is desirable to position construction joints at points of minimum shear. Shear keys, diagonal dowels, or the shear transfer method (ACI Code 318-11, Section 11.7) may be used.
How many types of joints are there in a concrete structure?
1. Construction joint – These joints in the concrete structure are designed to separate the large concrete mass work into a divisional pattern. These joints’ main purpose is to divide the large voluminous concrete work in a specialized way so that there would be no problem with in-work during construction as well as the structural strength of structure wouldn’t be affected. At such time a construction joint also may induce. The unfavorable condition generally seizes the work, and thus the part of concrete in structure might get harden with time. Thus such old concrete (harden concrete) and new concrete to be placed during the resume of work are necessarily separated by unintentional instructions joints.
In such a situation such a construction joint is specially named as “Cold joints”. However such a joint must be consulted with the structural engineer, and cannot be randomly made. The engineer studies the stress conditions at that point and only decides whether to keep there joint and continue to work or not.
If joints on such points are analyzed to be not feasible then, the whole concrete work done previously might need to be demolished. The construction joint is generally adopted in long construction works as the formation of very large slabs, in construction of long retaining walls along the road, irrigation channels, etc.
- The construction joints should not be located near the centroid level of section as there transverse shear stress is very high.
- The construction joints are provided with “keys” at suitable spacing.
- The keys are interlocking structure made within the end of construction at the joint.
- In resuming the work at joint (especially cold joints) the surface of the joint must be cleaned.
The construction joints are needed to be supplied with the load transfer device if the entire load is to be distributed overall structure. This generally happens in the rigid slab where there is a high amount of traffic movement. At such conditions, they are connected with dowel bars and tie bars.
- Butt type
- Tong and groove type
- Butt type with dowels
- Butt type with tie bars
Butt type with tie bars
Why do we need construction joints for beam construction?
Beam Construction Joints – When beams are constructed in two different stages, we have to provide construction joints. The type of construction joint is based on the span, load, and the location of the joint, etc. Smaller beams that transferring smaller bending and shear forces, the general joint could be provided without many details.
What are the four types of structural joints?
Types of joints in construction. There are basically four types of joints based on their function and construction features. They are listed as, Construction joint ; Expansion joint ; Contraction joint ; Isolation joint ; 1. Construction joint. These joints in the concrete structure are designed to separate the large concrete mass work into a divisional pattern.
What are the examples of joints?
– Planar Joints. Planar joints have bones with articulating surfaces that are flat or slightly curved faces. – Hinge Joints. – Condyloid Joints. – Saddle Joints. – Ball-and-Socket Joints.
What are the components of construction?
- Concrete. Concrete is one of the most fabulous building materials available,as it can be used for virtually every building project that you can think of.
- Metal. When working with concrete,metal reinforcements are normally added.
- Concrete Block.
- Bricks or Stones.
- Weather-Proofing Materials.
- Checking the Condition.
What are the different types of concrete joints?
- The Purpose of Joints in Concrete Slabs. As concrete moves,if it is tied to another structure or even to itself,we get what’s called restraint,which causes tensile forces
- Decorative Joints. A cleanly sawed joint detracts very little from the appearance of a stamped slab.
- Jointless Slabs.
- Load Transfer