What are the anchor bolts for

Updated:15-04-2020
Summary:

Design and selection of anchor bolts for concrete found […]

Design and selection of anchor bolts for concrete foundations:

 

An anchor bolts is used to fasten objects or structures to the concrete. There are many types of anchor bolts that consist of constructions that are largely reserved for manufacturing companies. All consist of a threaded end to which a nut and washer for the external load can be attached. Anchor bolts are often used in all types of projects, from standard buildings to dams to nuclear power plants. They can also be used to securely attach recessed slabs to a concrete foundation when used with a steel component.

 

The simplest anchor bolt is an anchor cast in place. As shown in Figure 1, most constructions consist of a standard hex screw that is poured into damp concrete before setting. There are other models, some consisting of a bent bolt with a hook on the end or some other type of bending. Anchor bolts cast in place are the strongest type of attachment, but casting is difficult and they are generally used only for heavy machinery mounted on cast concrete floors. Another use of this anchor bolt is to connect a building's concrete foundation to its wall. This makes the building earthquake-proof. There are currently several devices with which the anchor bolt to be fastened can be held and placed in the concrete. These devices are mainly made of composite plastic. Once the concrete has hardened, only mechanical and epoxy screws can be used. The epoxy screws are the strongest, but they can be very difficult to install because the epoxy has to be mixed according to exact specifications, the hole has to be very clean and the set time has to be monitored. In addition, there must be a strict test program. In the Big Dig project in Boston, these procedures were not carried out well, resulting in a large concrete slab being crushed by a driver.

The anchor bolts are an important connection between the equipment and the foundation. Unfortunately, designers often overlook important points regarding anchor bolts, such as B. their length and strength and the amount of preload. Anchor bolts as well as other parts of the support system such as sole plates and washers can be one of the main flaws in new construction projects. The error usually occurs in the first year of operation. Although the number and size of the anchor bolts is determined by the device manufacturer, the length, configuration and construction material are in the hands of the foundation designer. Figure 1 shows good and bad designs.

 

Length: Short anchor bolts have always caused problems with the foundations of compressors. This often leads to horizontal cracks in the foundation. The best method today is to make it as long as possible and finish it in the concrete mat under the concrete foundation. In this way, they do not contribute to horizontal cracking and have the additional advantage of adding a post-tensioning effect.

 

Material: The anchor bolts for every dynamic machine must not be too strong. Today, ASTM A-193 steel anchor bolts with a yield strength of 105,000 psi are not much more expensive than semi-solid steel. Since the need for high clamping forces for compressors is recognized, alloy steel screws according to ASTM A-193 offer the required capacity without having to go through a larger anchor bolt.

 

Adjustable supports are the system of choice nowadays because they eliminate a potential initial misalignment problem that occurs from time to time with full bed injections. Adjustable systems also achieve optimal hot operation because the frame can be realigned to correct the orientation changes that occur when the device warms up during the first 100 hours of operation.

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