CEMP-E
TI 809-26
1 March 2000
CHAPTER 7
WELDING TO EXISTING STRUCTURES
1. GENERAL.
When welding to reinforce existing structures, several areas require investigation and, in some cases,
specific instructions. Other than load analysis of the structure to design the connections, several welding
issues arise. These include weldability of the existing steel, the reduction of strength to existing members
when being heated or welded, and the welding to existing weld deposits of unknown origin or made with
FCAW-S electrodes. AWS D1.1 Section 8, and its supporting Commentary, provides applicable code
provisions.
2. DETERMINING WELDABILITY OF EXISTING STRUCTURAL STEELS.
a. Investigation. Investigation of weldability is generally warranted for buildings constructed prior to
1945, although structural steels were not manufactured specifically for welding properties until A373 and
A36 came into use in the early 1960's. The weldability of steels between these periods is generally
considered sufficiently weldable.
b. Carbon Equivalency.
(1) The most reliable method to establish chemical composition for determining carbon equivalent
values is to remove samples from various members at selected no- or low-stress locations, then
analyzed spectrographically for composition. Portable spectrographs may also be used, although only
optical emission spectrography systems currently provide sufficient accuracy for measuring carbon
content. The laboratory analysis report should list the quantities of each of the elements in the selected
carbon equivalent equation, even if the percentage reported is zero.
(2) Other methods, although less reliable, include spark testing and weld sample tests. Spark
testing applies a grinding wheel at approximately 5000 rpm to the steel, then observing and
characterizing the color and nature of the sparks off the steel. Weld sample tests include welding small
test plates to the steel, then destructively using a sledge hammer to break off the samples, if possible,
and observing the nature of the fracture.
3. WELDING TO OLDER STRUCTURAL STEELS.
The poorer the weldability of steel, the greater the need for higher preheat and interpass temperatures,
and the greater the importance of low-hydrogen welding. All welding to existing structures should be
performed with low-hydrogen SMAW electrodes or with other wire-fed welding processes. Minimum
preheat and interpass temperatures can be determined from AWS D1.1 Annex XI, or from technical
literature.
4. INTERMIXING WELD PROCESSES AND FILLER METALS.
a. FCAW-S Deposits. Self-shielded Flux-Cored Arc Welding (FCAW-S) weld deposits contain
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