The basis of the design of reinforced concrete frames for fully ductile earthquake performance, applicable to low buildings as well as to major structures, is outlined in terms of capacity design criteria now considered essential to prevent non-ductile failures and enable the building to survive earthquake attack.

Ductile coupled shear walls, ductile cantilever shear walls, and less ductile "category 6" shear walls comprise three basic shear wall types included in categories 3, 4, 5 and 6 of Table 5 of the earthquake provisions of the New Zealand Loadings Code. Seismic resistance of these shear wall types, when fully cracked with reinforcement at or near yield where applicable, is discussed relative to code provisions. Reinforcement requirements are outlined, using capacity design criteria for ductile walls, and load-factor methods for "category 6" shear walls requiring distributed vertical and horizontal reinforcement to control cracking.

Detailing for ductility in reinforced concrete earthquake-resistant structures and the risk of non-ductile failure at lap splices of the larger sizes of reinforcing bars have resulted in increasing use of full-strength butt welds of reinforcing bars. The benefits to be gained from eliminating long lengths of lapping bars and reducing serious congestion are overshadowed, however, by the time and cost (both direct and indirect) involved in making arc welds on site and the necessity for special supervision and testing of the work.

The paper defines full-strength butt welded bar splices and recognises their suitability
 for earthquake-resistant reinforced concrete structures detailed for ductility. Aspects of the successful use of the
pressure-gas process on an eight-storey shear
core building are reported. Essential features
 of a pressure-gas technique developed for
making full-strength butt welds on site are
described. The significance of a band of
 decarburised steel occurring at the weld interface is discussed, and provisions for its control are indicated. The paper gives test methods and criteria for quality control and acceptance purposes, with reference to a detailed Specification and "Statement of Technique and Equipment” under which the technique is now in principle accepted by the New Zealand Ministry of Works. Proving tests using the technique are reported, and a metallurgical report by R. M. Robb on the test welds, including micro-photographs, is appended. The paper concludes by indicating the practicability of making full-strength butt welds of HY60 bars by the pressure-gas process.

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