This search bar will answer most questions

Hilti Epoxy and Overturning

Hilti Epoxy and Hold Down Installations

 

Hitli HY 200 is the epoxy of choice when installing hold downs on shear walls because of its low cost, high strength, and fast drying time which allows the technician to tighten the hold down bolts after 45 minutes.  This epoxy however does have limitations, not because the epoxy is  inadequate, but because the bond between the concrete and the steel hold down bolt has its limitations.

The red arrow below points a “bond strength” of 2290# for Hilti epoxy when it is used to bond a 5/8″ allthread rod embedded 12″ into the concrete, 2 inches away from the face of the concrete, and 4 inches away from the end of the concrete.  This placement scenario of an epoxied steel rod is common when shear walls are placed at the end of a wall or are placed next to a garage door opening or at a foundation corner.The red arrow represents the bond strength between the epoxy to the concrete.  The concrete break out strength represents the actual strength of the concrete and in this case is only 1023#.

The concrete break out strength is the weakest point of the epoxy bolt hold down connection and this value must be further reduced by dividing by 1.4 because the performance of concrete is evaluated using a system call the Load and Resistance Factor Design (LRFD), while retrofitting of homes uses the Allowable Stress Design method of evaluating concrete.  In order to convert the LRFD  value into an Allowable Stress design it must be divided by 1.4.  Once this is done the concrete break out strength is only 735#.  Given that the average shear wall has an upward pull of 550# per linear foot, the overturning force will severely damage most shear walls.  The best way to reduce this is by increasing the length of the shear walls.

Hilti

 

 

 

 

 

 

 

 

In this second scenario the red arrow points to the “bond strength” of Hilti epoxy when it is used to bond a 5/8″ allthread rod embedded 12″ into the concrete,  2 inches away from the face of the concrete, and 2 feet  away from either end.  This is seen when the shear wall is placed away from the ends of the foundation.   In this case the break out strength is shown by the blue arrow at 1871#.   If we divide 1871# by 1.4 we get 1,336#, much better than if we had placed the same size shear wall at the end.

Hilit 2

 

Below are two pages from a holddown manufacturer’s catalog and shows where the two failure points can occur. The first image shows where hold downs fail.  The top arrow point to where the hold down steel to wood connection can fail.
The bottom arrow shows where the allthread to concrete connection Hilti epoxy connection can fail.

The table rates the failure point of the wood to hold down connection in pounds of tension forces trying to pull the steel and wood apart as the shear wall trys to overturn.  The weakest one made is the HDU2 which will fail at 3072#.  The strength of this wood to steel connection exceeds the 2252# provided for by the epoxy which means the failure point will be in the epoxy.  In practical terms, this means there is no point in using a hold down greater than an HDU2 or designing a shear wall where the uplift forces will exceed 2252#

HDU Three

Hold Down

Areas Served

San Jose,Sunnyvale, Fremont,Oakland,Berkeley
And Surrounding Areas
408-664-6355
510-548-1111

Member

eeri-logo icc-icon
Structural Engineer's Association Icon

License Info

Works' Comp RWCC64393236
Contractors Lic #558462
Bond #SC6334450
Liability Ins PCA 1045011
Link to Contractor's License Board