Steel pieces are a material that is used in many structural strengthening applications. Recently, Restruction Corporation used rolled steel plates to confine a series of reinforced concrete bridge columns. The rolled plate formed a steel jacket. Fabrication tolerances of the steel are very demanding. A minimum 1” and maximum 1.5” space between the existing concrete column diameter and the inside face of steel is specified for the application of the steel jackets. Prefabricated steel pieces are erected in two pieces and required a full penetration weld, full height each side completed the steel application sequence. The annular space was grouted with high compressive strength cement grout to transfer the column loads into the steel jacket when needed. Confinement of in-adequate reinforcing steel lap splices in the column changed the height of each jacket dependent upon the location of the splice. A final coat of paint was applied for added protection.
This Hotel Parking Garage, constructed in the 1970’s, was badly deteriorated due to years of water intrusion. Snow melt off of vehicles and routine cleaning contributed to the intrusion. Located in Downtown Denver Colorado, this 140,000 sf, 5 level double tee constructed garage repair project consisted of 4 major work phases.
The first repair phase was the precast concrete members of the structure. The repairs needed due to corrosion of reinforcing in the garage’s double tee beams, inverted tee beams, and structural columns required a widespread shoring scheme, prior to excavation. In order for the shoring to distribute the loads properly level by level, it was required that the shoring in the garage be shored down to grade. In an effort to expedite the structural precast concrete repairs, Restruction Corporation utilized 72 shoring towers throughout the project. It was imperative at the beginning of the project that the garage remained operational for the Hotels guests. The project team was able to sequence the repairs with minimum impact to the hotels day to day operations. These major structural repairs were completed using the following repair methods: concrete excavation and replacement, shear crack epoxy injection, installation of a double tee stem shear section enlargements, structural rebar replacement, and bearing pad removal and replacement.
What I would like to do is give you some pointers based on some of the failures and successes we have gone through to qualify ourselves. (For specifics go to the rebar welding qualification in section-6 of the AWS D1.4 code for Structural Welding Reinforcing Steel). I’ll describe some basics of what is required for a company and a welder to get qualified to weld rebar. Unlike the structural welding certification which is relatively simple. Rebar welding and qualifier testing requirements can be confusing and difficult which can make it easy to make a mistake when designing a rebar welding qualifier, or testing. If you put some thought to it and look ahead at what you might be required to weld you can save yourself time and money by doing it right once.
There are three processes described in the code; SMAW-shielded metal arc welding, GMAW- gas metal arc welding and FCAW- flux cored arc welding. The process we use for rebar is SMAW (stick welding) so for this paper I will be referencing SMAW.
Qualifying under the AWS D1.4 code there are two primary areas you need to focus on: