Easy-to-Install, Pre-Compressed QuickTie Walls Perform Better
Originally published by the following source: Quick Tie Products, Inc. — October 9, 2017
The following article was produced and published by the source linked to above, who is solely responsible for its content. SBC Magazine is publishing this story to raise awareness of information publicly available online and does not verify the accuracy of the author’s claims. As a consequence, SBC cannot vouch for the validity of any facts, claims or opinions made in the article.
Conventional anchoring systems provide resistance to uplift by “reacting” to the uplift load as it is being applied. The uplift force applied at the roof level is a tensile force, transmitted through the intervening floors, walls and connections to the foundation. As the uplift force is applied, the conventional hardware is loaded through a system of nails, studs, straps, tension devices, bolts and foundation anchors. In reality, the conventional system relies on the ability of the structural wall, and the included construction hardware devices to be “stretched”. As the uplift force increases, the amount of “stretch” is also increased. Each joint or connection in the wall is stretched a finite amount, causing some components to separate. As the uplift load increases the separations become larger. The accumulation of these separations may cause undesirable cracks to occur in the interior and exterior finish materials.
Another phenomenon occurs in wood frame construction. The components of the wall system shrink. The amount of shrinkage is dependent on the selected framing materials. Wood studs do not shorten appreciably along their length when the temperature and/or the moisture content are varied. Horizontal framing members, however, may shrink considerably across their width as the moisture content is reduced to an ambient condition.
When supported by walls, the shrinkage of the joists or other horizontal framing members must be considered. The use of conventional construction hardware does not address this condition.
Another factor to consider is the inadvertent gaps between adjacent components “built in” during construction. The various materials vary in size, some because they are manually cut resulting in slightly different lengths from piece to piece and others because they came from different sources or with varying moisture content. The degree to which the adjacent components are drawn tight during construction must be addressed. Joists, for example, will not bear flat at both ends if the joist is warped. Likewise, pneumatic nailing guns will not draw warped or twisted top plates tight against studs or lower top plate. This leaves small gaps between the components. As the self weight of the structure accumulates during construction, these inadvertent gaps will close.
Conventional construction hardware is usually installed before the gaps are closed. When the uplift force is applied, it will “stretch” the wall to the same height it was when the hardware was installed (prior to the gaps closing, Figure 1). Only then can the hardware begin to provide resistance. In reality, the “slack” in the wall must be removed before the hardware can do its job. Conventional construction hardware does not address this condition.
Likewise, threaded rod applications do not address the problem of building compression due to dead loads (also known as “settling”, Figure 2). Companies within the threaded rod industry, has attempted to address this problem through the use of take up devices as outlined in the ICC-ES AC391 adopted.
Pre stressing or pre-compressing the walls does address these concerns. Tensioned Quick Tie (cables), provides a pre-compression force to the wall into which they are installed. The wall components are also subjected to a greater compressive load than walls constructed with conventional hardware. Even when the wall “shrinks” or is reduced in height for whatever reason, the force on the top plate from the Quick Tie is only reduced slightly. By applying a higher tensile force to the Quick Tie when it is installed, the anticipated shortening is compensated for. Then, as the wall shortens, the force from the Quick Tie is reduced. When the anticipated shortening is reached, the initial pre-compressing force has been reduced to the design force.
The real advantage of pre-compressed walls is that there can be no vertical displacement or deflection of the top plate until the magnitude of the pre-compression force is exceeded. That event is usually the design wind or earthquake.
Stated another way, no vertical movement will occur in the top plate of the top floor until the design wind velocity or seismic forces has been exceeded.
And finally, because the tension applied to the Quick Tie at the time of construction exceeds the design load, the pre-compressed installation has been proof tested to exceed the design load. No conventional or rod system on the market does this without the addition of other parts which are specific to compensating for shrinkage or building compression.
FOR MORE INFORMATION CONTACT US OR VISIT OUR WEBPAGE: www.quicktieproducts.com
Quick Tie Products, Inc.
13300 Vantage Way
Jacksonville, FL. 32218
Phone: (904) 281-0525
Fax: (904) 281-0526