August_1971 — Page 32

On-site jointing method

for H shape structural columns

Shape and dimensions of the NHI joint

Backing strips, Tab

H.T. bolt

Web splice plate

-type spacer

Hatched

Welding length

Max. 650mm

Web splice plate,

H.T. bon

Harrow

squers-groove

Web surface

Cross-section of column - Plan

Assembled joint before welding

Web fastening with splace plates and H.T. bolts

Erection piace

Automatic horizontal welding of Bangs by the MIG (Gas metal-arc) welding equipment

Erection piecE

Gap 14:2.5

Tab Backing strip

B

Applicable flange thickness

Flange surface

A

Narrow square-groove

B

#

H shape steel column

Web splica plata

HLT. bolt

Backing strip, Tab

C

HHHH

CONVENTIONAL METHOD

Notes:

Complete

1. In case the web portions of the upper and lower H- shaped columns are preferably joined by welds instead of bolt fastening (A), a spacer of square type steel plate having the width greater than the thickness of the webs is interposed between the two steel columns (B).

Far East BUILDER, August 1971

NHI METHOD

Partial

2. When only a partial penetration is required because of the existence of small tensile stress throughout the

whole thickness of the flanges at the column joint, the

depth of the square groove can be reduced to facilitate partial penetration welding by inserting additional

spacers to the gaps between flanges of both sides of the column section (C).

IHI (Ishikawajima-Harima Heavy In- dustries Co., Ltd.) of Japan has recent- ly developed a new jointing method for the H shape steel columns widely used for the framework of high rise buildings. Known as the NHI method, it rationalises and simplifies factory machining and makes on-site welding quick and easy.

Complicated edge preparation of H shape steel columns is eliminated and, for the first time, fully automatic on- site welding of the H columns becomes possible with the new automatic wel- der developed jointly by IHI and Kobe Steel, Ltd.

In the NHI method, the connecting faces of the H shape columns are cut at right angles and a thin I type steel spacer is inserted between them to make the gap necessary for welding. This eliminates factory machining of the groove and the web scallop (a gap through which is passed a chill strip) on the 30-65 mm thick flanges of the columns at a considerable saving of time and labour. In the new method the H shape column end can be cold sawed at the factory. Jointing of the webs, however, uses splice plates and high-tensile strength bolts, as in con- ventional methods.

Complicated welding which requir- ed tens of bead layers to be placed on grooves on the joint with manual or semi-automatic welding equipment is not necessary, and the narrower groove uses less metal and consequent- ly cuts on-site welding time to 1/2 or 1/3 of the previous 3 to 5 hours. Fully automatic welding gives uniform and stable results without skilled welders. while the joint is improved because the peripheral zone around the weld is less subject to heat, and deformation and brittleness of the parent metal are avoided.

The NHI method fulfils a long- standing requirement of the construc- tion industries for quick, reliable and cheap on-site welding. It is expected to completely replace the present welding method.

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