Abstract
1. Purpose SRC stub columns of mechanics behavior very complicated, mainly because steel plate and reinforcement concrete ,etc. composite effect of material, difficult to separate for evaluation. Specifically, it is very difficult to utilize the test to get confine of behaviors to concrete with “ Steel shape” and “ Hoop reinfocement” directly too. This research according to encased steel reinforced concrete stub Columns to the project in Taiwan commonly, under monotonic axial load test of large-diameter fully-encased SRC stub column specimens, discussion concrete in stubs is subject to confinement of behavior “ steel flange”, confined concrete of possible shape, understand SRC stub columns uses the composite effect of the material , and then the design code of SRC construct in Taiwan, discussion on SRC stub columns of the reasonable requirement of hoop reinfocement, and the corner crossties is a construction detail, hope a rise in constructional and economically SRC stub columns, cooperate with the experiment results, propose the revision suggestion of the SRC construct design code of clause. 2. Method and Steps Research this plan 26 large-diameter fully-encased SRC stub column specimens, categorized into A, B, AWS, S, SRC-A and SRC-B series, were constructed and tested under monotonic axial load. The dimension of specimens has such three kinds as 670×670 mm , 560×560 mm and 450×450 mm ,etc. , plan this design parameter of specimens of research, including the section shape of confined concrete is enclosed by steel shape, width of steel flange and depth of steel shape ,etc. by observing and discussing the axial load behavior and failure mode of SRC stub column specimens. 3. Main Finding According to this research experimental result to show that, sum up several important discoveries and do the following explanation. 1. The design code of SRC construct in Taiwan regulate that nominal strength the evaginated formula, SRC stub columns of deep steel shape, that display good consistency with the experimental result, with the increase of the minimum requirement for hoop reinforcement, that can improve SRC stub columns axial bear behavior which seismic ductility. 2. Steel flange surrounds concrete, supplying effective confined result, the behavior of stress-strain of confined concrete, it will not follow that the width changes of steel flange, cause the obvious difference, and range of steel shape confine concrete configuration, should be circular confined mode. 3. In the design method of the requirement for hoop reinforcement of SRC stub columns, requirement for hoop reinforcement of design code of AISC (2005) of U.S.A. is the most conservative, this research discusses five kinds of design methods, all meet the minimum demand for experiment axial displacement ductility ratio, so the minimum requirement for hoop reinforcement of SRC stub columns, design formula which reduce to strength reduction approach that it can be reasonable. 4. " Modified Strength Reduction Design Approach" proposed in this research, extra coefficient of strength to steel flange confine concrete mainly, propose adjusting from 0.2 to 0.4, and revise the range of confine concrete configuration in SRC stub columns, should be circular confined mode. This method can consider steel shape of SRC stub columns shares the contribution of axail load at the same time too, and confined effect to the concrete, can save 20.7% of the amount of hoop reinforcement through estimating, can rise in constructional and economically SRC stub columns. 5. The corner crossties of SRC stub column, that install the standard hook of 90° in both ends at the same time, and ensure that the length of hook must be greater than 8 times of diameters of hoop reinforcement, nearby should effective fix rebar, full developed helping confined effect of concrete in SRC stub columns, should to rise the feasibility of constructing by a wide margin. 4. Major suggestion Short term Suggestion –Propose “Modified Strength Reduction Design Approach ”that can reduce the minimum requirement for hoop reinforcement of SRC stub columns reasonably. Major Office：Construction and Planning Agency Ministry of Interior Associate Office：Architecture and Building Research Institute Ministry of Interior, The Architects Association, Professional Civil Engineers Association, Professional Structural Engineers Association, and the Civil, Architecture. This research was proposed “Modifiable Strength Reduction Design Approach ”, that can consider the contribution of steel shape of SRC stub columns bear that axial load at the same time, and the effects of confinement to concrete with steel shape, that can reduce the amount of hoop reinforcement of SRC stub columns effectively , can save 20.7% of the amount of hoop reinforcement through estimating, can rise in constructional and economically SRC stub columns. Short term Suggestion - Propose the corner crossties of SRC stub column,that install the standard hook of 90°in both ends at the same time. Major Office：Construction and Planning Agency Ministry of Interior Associate Office：Architecture and Building Research Institute Ministry of Interior, The Architects Association, Professional Civil Engineers Association, Professional Structural Engineers Association, and the Civil, Architecture. The design regulation of corner crossties of SRC stub column, one side is a standard hook of 135°, another side is a 90°, a lot of building engineers make difficulty in response. This research proposes the length of hook must be greater than 8 times of diameters of hoop reinforcement, then the corner crossties is a amendable standard hook which install 90°of both ends of corner crossties, in order to rise the feasibility of constructing. Short term Suggestion - The regional configuration of confined concrete by the steel shape, should be a confined mode of circular. Major Office：Construction and Planning Agency Ministry of Interior Associate Office：Architecture and Building Research Institute Ministry of Interior, The Architects Association, Professional Civil Engineers Association, Professional Structural Engineers Association, and the Civil, Architecture. Steel flange surrounds concrete, supplying effective confined result, range of steel shape confine concrete configuration, should be circular confined mode, and then to collocate the revision of " Modified Strength Reduction Design Approach ", that reduce the minimum requirement for hoop reinforcement of SRC stub columns reasonably that can be effective.