Buckling Length of Unbraced Frame Columns

In the design of steel columns in unbraced frames, the current AISC specification commentaries from both LRFD and ASD contain an alignment chart to determine the K factor for a particular column. The K factor is based on the effective length concept where K factors are used to equate the strength of a compression member of length L to an equivalent pinended member oflength KL subjected to axial load only. The unbraced frame alignment chart is a graphical representation of a transcendental equation of a buckling solution of a subassemblage. This solution involves several assumptions limiting the use of the alignment chart to idealized cases not necessarily satisfying a particular practical situation. The aim of this study is to I) compare K factor values from frame instability analysis usmg structural software with values from the alignment chart in situations where the assumptions of the alignment chart are violated and 2) suggest application of appropriate known solutions to particular situations in which violations of the assumptions occur. Situations investigated are: variations in bay width, variations in column moment of inertia, variations in loading, and variations in column height. The nomograph perfom1ance was found to be relatively insensitive to bay width variation. Variations in column moment of inertia and column loading lead to large inaccuracies in the nomograph K factor values but Lui's method handled these cases well. The nomograph performance was found to be most sensitive to column height variation. Configurations with large variation in column height require system stability analysis to obtain accurate K factors

Compressive creep of kenaf bio-fibrous concrete composite under one dimensional stressing

The experiment was designed to investigate the creep of concrete specimens under one dimensional compressive principal stress. The equipment for producing the stress and the gauges for measuring the strai ns are described. T he results of the experimental study illustrated the effects o f the inclusion of Kenaf fibre and age at loading on creep signature of the concrete. Creep tests were performed in the drying ro om with 50±4% relative humidity . Kenaf fibres were used at 50mm fibre length and volume fractions of 0.5% by volume of mix. Results available for specimens subjected to 25 and 35% of the strength in compression were presented. The final discussion compared the effect of Kenaf fibre inclusion and age a t loading of specimens subjected to compressive creep at two different stress levels. Low modulus fibrous concrete such as Kenaf bio - fibrous concrete composite demonstrated somewhat greater creep strains than the plain concrete, but the deformation behavio ur shows improvement in ductility

An evaluation of the interfacial bond strength of kenaf fibrous concrete and plain concrete composite

The deterioration of concrete structures is a matter of critical concern as it threatens the durability and strength of concrete structures. Kenaf fibrous concrete composite (KFCC) can be used with advantage in new structures such as precast elements, as well as the strengthening, repair and rehabilitation of old structures to improve their durability properties. These structures are composite components, with parts as Plain concrete (PC) and others as KFCC. This study, therefore, investigated the interfacial bonding behaviour between KFCC and PC. Shear, tensile and compressive tests were carried out to measure the bond strength in shear, direct tension and compression respectively for PC to PC, PC to KFCC and KFCC to KFCC interface. Three different types of concrete grade (25, 35, and 45 MPa) were produced for the KFCC and one type of concrete grade (35 MPa) for the substrate PC. The outcome of the test showed that KFCC had an excellent interlock with the surface of the PC substrate, and thus, gives bond strength greater than the strength of PC. New concrete with the highest concrete grade of 45 MPa ensued in high compressive, tensile and shear bond strength

Behavior of perforated cold-formed steel sections with trapezoidal web stiffeners

Experimental studies is performed to examine the strength and behavior of perforated cold-formed steel sections with edge and web stiffeners subjected to compression loading. Axially compression load was imposed on fix ended short columns with various perforation series. There are total of 16 specimens was conducted as to observe possibility interaction between them essentially the stability capacity, buck-ling mode and behaviour. The results showed that the ultimate load of the cold-formed steel sections with edge and web stiffeners under compression varied significantly with the perforation position. Under the same condition, the ultimate load-carrying capacity of Σ-section members and conventional Csection members was increased by 10-20 %. The ultimate strength graphs are drawn as well as the failure modes are discussed for different cross-sections and perforations positions

Mechanical properties of kenaf fibrous pulverized fuel ash concrete

The main objective of the experimental work is to identify the mechanical properties of Kenaf Fiber incorporate with Ordinary Portland Cement (OPC) and Pulverised Fuel Ash (PFA) in the mix proportions of concrete. Kenaf Fibrous Concrete (KFC) and Kenaf Fibrous Pulverised Fuel Ash Concrete (KFPC) will be measured on physical and mechanical properties in order to investigate the suitability of this natural fiber as a composite material. A comparison of properties between these two composites will determine the density, workability, compressive, tensile, and flexural strength of the concrete. Eight different mixes with varying percentage of Kenaf fiber were prepared with 30N/mm2 strength at 28days ,56 days and 90 days. Short fiber with 25mm and 50mm length were randomly distribute in composite to enhance the tensile and durability. PFA was obtained by the process of burning in the Power Station Coal Ash at Tanjung Bin, Johor. The unburning powder from the process is called as a PFA generally suitable for cement replacement in the concrete mix. The pozzolanic reaction will improve the adhesion of cement gel, hence increased the properties of concrete in a long-term strength development. The result shows that the inclusion of Kenaf fiber improve tensile strength of composite, furthermore the 25% PFA mix increase the durability of concrete

Mechanical properties of kenaf fibrous pulverized fuel ash concrete

The main objective of the experimental work is to identify the mechanical properties of Kenaf Fiber incorporate with Ordinary Portland Cement (OPC) and Pulverised Fuel Ash (PFA) in the mix proportions of concrete. Kenaf Fibrous Concrete (KFC) and Kenaf Fibrous Pulverised Fuel Ash Concrete (KFPC) will be measured on physical and mechanical properties in order to investigate the suitability of this natural fiber as a composite material. A comparison of properties between these two composites will determine the density, workability, compressive, tensile, and flexural strength of the concrete. Eight different mixes with varying percentage of Kenaf fiber were prepared with 30N/mm2 strength at 28days ,56 days and 90 days. Short fiber with 25mm and 50mm length were randomly distribute in composite to enhance the tensile and durability. PFA was obtained by the process of burning in the Power Station Coal Ash at Tanjung Bin, Johor. The unburning powder from the process is called as a PFA generally suitable for cement replacement in the concrete mix. The pozzolanic reaction will improve the adhesion of cement gel, hence increased the properties of concrete in a long-term strength development. The result shows that the inclusion of Kenaf fiber improve tensile strength of composite, furthermore the 25% PFA mix increase the durability of concrete

Behaviour of perforated built-up cold-formed steel sections with edge and web stiffeners

This paper presents the experimental investigation of various perforation positions influence on C-sections cold-formed steel with edge and web stiffeners assemble as built-up open section subjected to axial compressive load. The built-up sections been setup as back-toback by using self-tapping screws connected at web on two longitudinal lines of 100 mm spacing. The sections is then fabricated as 600 mm short column structures with both ends are fix-welded to 20 mm thickness of bearing supports. Total of 16 nos of specimens consist of both conventional and modified 1.2 mm thickness built-up C-sections with the sequence positions of elongated circle perforations whether as absent or present as in single or multiple openings. The strength of the columns as the results of ultimate load by caused of the location of perforation even if at middle section or near end section are tabulated. The results show that the establishment of stiffeners may increase the strength of the column. However, the effects of perforation when as a multiple openings and the position is closer to the support will reduce the strength