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When is it safe to place a construction load on a concrete structure?

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Discover the crucial factors to consider before placing a construction load on a concrete structure in the US. Learn about the necessary waiting time, curing process, and structural assessments to ensure safety and durability.

When embarking on a construction project, one of the key concerns is determining when it is safe to place a construction load on a concrete structure. It is essential to understand the waiting time, curing process, and structural assessments required to ensure the safety and longevity of the structure. In this article, we will delve into these factors, providing valuable insights to contractors and individuals involved in construction projects in the US.

Understanding the Waiting Time for Concrete Structures

  1. The Initial Setting Time

    • The initial setting time refers to the period required for the concrete mix to transform from a liquid state to a solid state.
    • This process typically takes around 4 to 6 hours, but it can vary depending on factors such as temperature, humidity, and the type of concrete mix used.
    • During this stage, it is crucial to avoid any load-bearing activities, as premature stress can compromise the structural integrity.
  2. The Final Setting Time

    • The final setting time indicates when

Removal of formwork.

Reshoring shall not be removed until the concrete being supported has attained adequate strength to support its weight and all loads in place upon it.

What is the OSHA standard 1926.701 B?

The standard, 29 CFR 1926.701(b), states: "all protruding reinforcing steel, onto and into which employees could fall, shall be guarded to eliminate the hazard of impalement." The key words are "to eliminate the hazard of impalement." Exposure to impalement is always a consideration when employees are working above

Which of the following is an accepted method of determing when it is safe to remove concrete formwork?

After pouring and finishing the slab, you should wait 24-48 hours before removing concrete forms. You can remove the formwork once the concrete has enough strength to keep it from cracking. Concrete naturally contracts as it cures, so it should pull away from the forms and make them easier to remove.

What are the most frequently cited serious violations of the concrete and masonry construction standard?

Some of the most cited serious violations of subpart Q include: • Failure to protect employees from impalement when rebar is not capped or covered • Failure to establish a limited access zone (LAZ) to limit the number of workers in the danger zone where a masonry wall is under construction • Failure to brace

When can concrete formwork be removed?

Removing formwork

When the concrete has enough strength to support the weight it must bear (seven days) strip the forms away. Do not use a metal tool against the surface to pry off forms because you may cause damage.

When a restricted zone shall be established whenever a masonry wall is being constructed?

F. 02 A restricted zone shall be established whenever a masonry wall is being constructed. The restricted zone is created to keep masons and other tradesmen away from a wall under construction when winds exceed critical velocities until the wall is completely tied into the rest of the structure.

What is the OSHA standard for controlled access zone?

The control lines used to define the controlled access zone must be between 6 feet and 25 feet from the leading edge and must be attached on either end to a wall or guardrail system. If the control line is attached to a guardrail system, this system must comply with the requirements in §1926.502(b).

Frequently Asked Questions

What is the limited access zone of a masonry wall?

The limited access zone shall be equal to the height of the wall to be constructed plus four feet, and shall run the entire length of the wall.

What is OSHA requirements for rebar caps?

Proper protective rebar caps should be at least 4” square or, if they are round, they should have a 4.5 inch diameter. Some rebar caps are too narrow or not steel-reinforced.

What OSHA standard covers construction safety?

1910.12 - Construction work. Occupational Safety and Health Administration.

What is the limited access zone for masonry construction?

Hear this out loudPauseThe limited access zone shall be equal to the height of the wall to be constructed plus four feet, and shall run the entire length of the wall.

What are the design specifications of masonry wall?

Compressive Strength of Mortar

Compressive StrengthCement-lime-sand with or without air-entrainmentMasonry cement-sand
M121:0 to 1/4:3
M61:1/2:4 to 4.51:2.5 to 3.5
M41:1:5 to 61:4 to 5
M21:2:8 to 91:5.5 to 6.5
Oct 30, 2022

Which of the following are considered masonry construction?

The common materials of masonry construction are bricks and building stone such as marble, granite, and limestone, cast stone, concrete blocks, glass blocks, and adobe. Masonry is generally a highly durable form of construction.

FAQ

What is the limited access zone for masonry OSHA?

The limited access zone shall be equal to the height of the wall to be constructed plus four feet, and shall run the entire length of the wall. The limited access zone shall be established on the side of the wall which will be unscaffolded.

What must be capable of supporting 2.5 times the load being lifted?
Jacking equipment shall be capable of supporting at least two and one-half times the load being lifted during jacking operations and the equipment shall not be overloaded. For the purpose of this provision, jacking equipment includes any load bearing component which is used to carry out the lifting operation(s).

What is the OSHA standard 29 CFR 1926.701 B?

The standard, 29 CFR 1926.701(b), states: "all protruding reinforcing steel, onto and into which employees could fall, shall be guarded to eliminate the hazard of impalement." The key words are "to eliminate the hazard of impalement." Exposure to impalement is always a consideration when employees are working above

When is it safe for you to place a construction load on a concrete structure

No construction loads shall be placed on a concrete structure or portion of a concrete structure unless the employer determines, based on information received 

Who can determine when formwork can be removed from cast in place concrete?

Always check with your site engineer to confirm the exact timeline your concrete forms require to cure properly. The following can be are general rules for Ordinary Portland Cement (OPC): Walls and columns can be removed after about 24-48 hours.

Which of the following is an accepted method of determining when it is safe to remove concrete framework?

After pouring and finishing the slab, you should wait 24-48 hours before removing concrete forms. You can remove the formwork once the concrete has enough strength to keep it from cracking. Concrete naturally contracts as it cures, so it should pull away from the forms and make them easier to remove.

When is it safe to place a construction load on a concrete structure?

What are some of the requirements that must be met when single post shores are used on top of another?

The single post shores shall be vertically aligned. The single post shores shall be spliced to prevent misalignment. The single post shores shall be a adequately braced in two mutually perpendicular directions at the splice level. Each tier shall also be diagonally braced in the same two directions.

Who must determine when forms and shores may be removed?

Forms and shores (except those used for slabs on grade and slip forms) shall not be removed until the employer determines that the concrete has gained sufficient strength to support its weight and superimposed loads.

What is included in the construction of masonry walls?

Masonry is the craft of building a structure with brick, stone, or similar material, including mortar plastering which are often laid in, bound and pasted together by mortar; the term masonry can also refer to the building units (stone, brick, etc.) themselves.

What is the process of masonry construction?

Masonry is a construction technique that involves stacking materials, such as bricks, stone blocks or concrete blocks, on top of one another to build structures or walls. Masons layer these materials using mortar , an adhesive paste that fills the gaps and binds materials together.

What must be done to masonry walls over 8 feet?

All masonry walls over eight feet in height shall be adequately braced to prevent overturning and to prevent collapse unless the wall is adequately supported so that it will not overturn or collapse. The bracing shall remain in place until permanent supporting elements of the structure are in place.

What should you do before starting masonry activity?

Before work begins, the mason should check to see that the line is level, tight, and will not pull out. Each mason working to the same line needs to be careful not to lay a unit so it touches the line. This will throw the line off slightly and cause the rest of the course to be laid out of alignment.

  • When is it safe for you to place a construction load on a concrete structure?
    • Construction loads must not be placed on a concrete structure unless the ______ determines, based on information received from a person who is _____ in 

  • How is lift slab construction performed?
    • Lift-slab construction, Technique whereby concrete floor slabs are poured on the ground, one on top of the other, and then lifted into place on top of columns by hydraulic jacks. Used for very tall multistory buildings, this method offers substantial savings in formwork.

  • How many employees are allowed under precast concrete members that are being lifted or tilted into position?
    • No employee

      No employee shall be permitted under precast concrete members being lifted or tilted into position except those employees required for the erection of those members.

  • What equipment raises a concrete slab in lift slab construction?
    • After the slabs have cured long enough to reach a prescribed strength, powerful hydraulic jacks mounted on top of the columns lift the slabs into their respective positions.

  • What are the OSHA requirements concerning the routing of concrete buckets being lifted by a crane?
    • (1) No employee shall be permitted to work under concrete buckets while buckets are being elevated or lowered into position. (2) To the extent practical, elevated concrete buckets shall be routed so that no employee, or the fewest number of employees, are exposed to the hazards associated with falling concrete buckets.

  • Who must perform slab designs in lift slab construction?
    • Lift-slab operations shall be designed and planned by a registered professional engineer who has experience in lift-slab construction. Such plans and designs shall be implemented by the employer and shall include detailed instructions and sketches indicating the prescribed method of erection.

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