●A Case of Utilizing Results

Quality Control and Designation of Specified DesignStrength for Structural Steel
Building Department
MUKAI Akiyoshi, Research Coordinator for Advanced Building Technology
Standards & Accreditation Systems Division
IWATA Yoshihiro, Senior Researcher, Dr.Eng.
(Keywords) Structural steel, quality control, specified design strength, uniform elongation, rupture elongation
1. Introduction
When using high-strength structural steel andother new materials as principal structural membersof buildings, the specified design strength requiredfor structural calculations (values forming the basis
for allowable stress, etc.) needs to be designated,accompanied by ministerial approval under Article
37 (ii) of the Building Standard Law pertaining to thequality of building materials. Until now, however,there has been no unified method of designating thespecified design strength of structural steel.
Therefore, we studied designation methods with aview to achieving unified operation by designatedperformance evaluation bodies, in addition toministerial approval. The outcome of this was that
we classified structural steel into categories based onyield ratio and uniform elongation, and presented aunified method of designating the specified design
strength for each category (referred to below as the“proposal for provisional treatment”). Now,
designations of specified design strength forstructural steel are being applied on the basis of thisproposal.
2. Outline of the proposal for provisional
treatment
The quality of structural steel is determined byvarious mechanical properties, the most importantones of which are yield strength, tensile strength, yieldratio and uniform elongation. In the proposal for
provisional treatment, steel materials are divided into
three categories – ductile, intermediate and elastic –taking the yield ratio and uniform elongation as scales.
The proposal focuses on three steel material products– thick plate, shaped steel and steel pipes – andspecifies methods of designating specified design
strength for each category. Fig. 1 shows an outline ofthe proposal for provisional treatment. Here, the yieldratio as the vertical axis represents the yield strengthof structural steel divided by the tensile strength,
expressed symbolically as σy / σu. The uniform
elongation as the horizontal axis represents permanentstrain in relation to tensile strength. The areas marked* in the graph are those that can be given leeway,
taking various factors into account.

Yield ratio

1.00

Area beyond the scope ofapplication for now*Areas given leeway”

Elastic materials
F=not designated, time-history response
analysis route F=min[0.70σu, σy]Piles, sub-beams, etc.

0.90

**
Intermediate materials
*0.80
*

3%

5%

Without experiments, etc. → Elastic materials
With experiments, etc. → Ductile materials
Possible up to F=min[0.75σu, σy]Ductile materials
F=min[0.70σu, σy]Uniform elongationF: specified design strength, σy: yield strength, σu: tensile strength

Target: thick plate, shaped steel, steel pipes(yield ratio with plate thickness less than 12mm is outsideregulation)

Figure 1. Schematic diagram of the outline proposal
for provisional treatment
In actual practice, quality control of structuralsteel is not based on uniform elongation but on
rupture elongation, and a conversion rule between
the two will be required when applying this proposal.
Therefore, NILIM and the Japan Iron and SteelFederation (JISF) carried out joint research on“Elongation performance of structural steel for
determination of specified design strength”, andexperimentally studied the relationship between
uniform elongation and rupture elongation ofstructural steel at varying levels of strength when thedimensions of the specimen were changed. The
outcome of this research has been published in a
NILIM Technical Note 1).
[References]
1) Nishiyama, Mukai, Iwata et al: Effect of dimensions ofspecimen on elongation of structural steel, NILIM
Technical Note No. 662
http://www.nilim.go.jp/lab/bcg/siryou/tnn/tnn0662.htm