The capacity analysis of wide flange steel section as beam-column elements

The design of the steel frame structure for beam, column, and beam-column elements usually takes several iterations to obtain optimum results that are safe, efficient, and economical. The problems that arise due to the number of iteration for the design process are the basis for this research. The research was conducted on 100 sections IWF and HCS which are consisted of 81 sections of IWF and 19 sections of HCS. The analysis was carried out regarding SNI 1729:2015. The results of this study are in the form of moment capacity graphs and tables of the axial capacity of steel sections as well as coefficients of m and U for beam-column design. Moment capacity graphs and tables of the axial capacity of IWF and HCS profiles produced could be used to reduce the number of iteration in designing safe and efficient steel profiles as beam, column, and beam-column elements. Analysis results show that the usage of the graphs and tables for the beam-column design process will reduce the number of iteration needed.


Introduction
Along with the development of technology in the field of construction, steel sections have become one of the options to be used as structural elements in building construction. This steel construction can be seen in today's buildings such as houses, factories, stadiums, hotels, and even other high-rise buildings [1].
There are various types and sizes of steel sections available in Indonesia, such as WF (Wide Flange) and HCS (Heavy Column Section). The WF section consists of I and H beam sections, wherein total there are 81 steel sections with different dimensions. The HCS section consists of 19 sections with different dimensions [2].
Various sections available on the market with different specifications make engineers carry out repeated iteration to obtain a section that is safe, efficient, and economical. The repeated iterations carried out by the engineers made the structural design process would be tedious and required a lot of effort to get an efficient steel section.
The results of this study will be design aids in the form of tables of axial capacity and nominal moments of IWF and HCS sections. These tools are then used in designing steel structures that are safe, efficient, and economical. By using this tool, there will be fewer experiments, so it doesn't take up much time and effort.

Steel Section
Steel material first appeared in the 19th century where steel is an alloy of iron and carbon. The carbon material found in steel is less than the carbon material in cast iron. The manufacture of large volume steel was first carried out by Sir Henry Bessemer, who received a patent from the British government for his findings in 1855 [1].
The first steel frame structure was the Home Insurance Company Building in Chicago [1].

Beam
Beams according to SNI 1729-2015 are nominal horizontal structural members that have the main function to withstand bending moments [3]. Beams are structural components that carry gravity loads, such as dead loads and live loads, beam structural components are a combination of compression elements and tensile elements [1].

Column
Columns according to SNI 1729-2015 are nominal vertical structural members that have the main function of resisting axial compression forces.
Compressive members are intended for structural members that carry centric compressive loads right at the center of gravity of the cross-section or column with only axial forces [4].

Beam-Column
Beams-columns according to SNI 1729-2015 are structural components that resist axial forces and bending moments.
Structural members sometimes the effects of the combination of axial forces and bending moments are not negligible, hence the combination of axial forces and bending moments must be considered in the design process of structural members. These structural members are often referred to as beam-column elements [1].

Research Methodology
The research was conducted by analyzing the crosssectional capacity of IWF and HCS steel sections as a beam, column, and beam-column elements. This research is applied to academic research and is carried out carefully, systematically, and continuously on each IWF and HCS (heavy column section) steel profile used for structural design purposes.
The data used in the analysis process are IWF and HCS sections which consist of 81 IWF types and 19 HCS types.

Section Capacity Calculation procedure
Calculations were made for the sections of compact web and compact flange, compact web of the non-compact flange, and compact web and slender flange for beam elements, while for column elements only non-slender sections were analyzed. The steps for calculating the section's capacity are carried out with the following procedure:

Column Action Calculation
The procedure is as follows: a. Controlling of slenderness ratio of web and flange of the sections to control the effect of local buckling.
b. Calculating the critical stress of the section (F cr ) c. Calculating the axial capacity of the column

Beam Action Calculation
a. Controlling the slenderness ratio of web and flange of the sections to the effect of local buckling b. Calculating the nominal capacity of bending moment based on lateral-torsional buckling criteria a) Section with compact web and compact flanges bending about its major axis, with categories of: Section with compact web and non-compact flange bending about its major axis. Beam-column analysis was carried out on three types of effective length factor (k). The three effective length factors consist of: 1. k=1, nominal moment capacity of the beam at span L compared to axial capacity at kL=L. 2. k=0,5, nominal moment capacity of the beam at span L compared to axial capacity at kL=0,5 L. 3. k=2, nominal moment capacity of the beam at span L compared to axial capacity at kL=2L.

Plotting of Nominal Bending Capacity Graphs of Beams
The nominal moment capacity graphs of the beam are formed from the relationship between the length of the

Composing Table of Section Axial Capacity and Coefficient of m & U
The value of the coefficients m and U is a multiplier coefficient that is used to obtain the equivalent Pu value for each section that will be used as a beam-column element due to the effect of bending moments. Pu equivalent is the ultimate axial value which is obtained from the combination of the ultimate axial capacity P u , the x-direction bending moment (M x ), and the y-direction bending moment (M y ) values. The equivalent Pu value is used as a determining value for the factored section axial capacity (∅P n ). A profile will be said to be efficient if the equivalent P u value of the structural element is close to the P n value of the structural element. The table of the axial capacity of sections and m & U coefficients will be summarized in tables as the result of the analysis process. Each table will contain the axial capacity of the section, the value of the M coefficient, and the value of the U coefficient for each IWF and HCS section. This table will contain the entire sections that have been analyzed. The table contains the axial capacity, the value of m, and the value of U from Lb = 0.5 meters to 15 meters for each steel grade.

Section Data
The data used in the analysis process are IWF and HCS sections which consist of 81 IWF sections and 19 HCS sections. The IWF sections are used in the analysis of beams, columns, and beam columns while HCS sections are used in the analysis of columns and beam-columns.

Bending Moment Capacity Graphs
Below are the samples of the results of the analysis of the bending moment capacity steel sections as beams The figures of bending moment capacity for each steel grade above shows that the value of the bending moment capacity in each section increases in proportion to the quality of the steel used. The greater the quality of the steel, the greater the moment capacity. The greater the quality of steel, the crosssection of the profile closer to the limit of compactness.      Axial capacity tables are used to determine efficient profiles for column and beam-column elements. The values of axial capacity, coefficient m, and coefficient U in the table are presented for a compact profile, with  a sample of Table 1.

Testing the Efficiency of Profiles as Beamcolumn Elements
The efficiency of the IWF steel section as a beamcolumn element can be tested with the interaction The interaction coefficient is very close to 1, hence the steel section obtained is efficient.

Conclusions
1. The resulting factored nominal moment capacity graphs (M n ) can be used as a reference in the process of designing efficient beam elements. 2. The table of factored axial capacity (P n ) and the resulting m and U coefficient can be used as a reference in the design process of beam-column elements to obtain efficient sections and reduce the iteration process.