Hollow Section Research Articles

The Effects of Various Adhesives on Multiple Types of Quasi‐Static Mechanical Properties of Rectangular and Square Aluminum Hollow Sections Filled with Composite Metal Foam Cores

For composite metal foam structures to be used as load‐bearing and energy‐absorbing elements, comprehensive testing should be done. Therefore, an extensive characterization of foam‐filled structures by various load types, such as axial and lateral compression, as well as three‐point bending, is carried out, aiming to differentiate the behavior of various cross‐sectional geometry foam‐filled hollow sections and the application of a tough epoxy adhesive and a ductile polysiloxane adhesive. Applying the epoxy adhesive improves the overall energy absorption by 10% during axial compression compared to the sum of the foam and empty hollow section. The application of the polysiloxane adhesive over the epoxy one increases the deflection at failure during three‐point bending by an average of 58%. The deformation and strength during axial compression and three‐point bending are hollow section dominated, while the foam core dominates the deformation and the strength during lateral compression for both produce composite foam‐filled hollow sections with epoxy and polysiloxane adhesive bonding.

Experimental investigation on cold-formed steel hollow sections with moderate heat treatment under combined compression and cyclic lateral loads

This paper presents an experimental investigation on cold-formed steel rectangular and square hollow sections (RHSs and SHSs) with subsequent heat-treatment under combined compression and cyclic lateral loads. A total of 25 specimens designed with different parameters, including slenderness ratios (b/t and d/t) and axial load ratio (n) ranging from 0 to 0.5 were tested. Material tests were carried out to confirm the material ductility requirements stated in Eurocode being reached. Failure modes, moment-rotation curves, secant stiffness, energy dissipation and plastic hinge length presented were analysed. In addition, deformation capacity was evaluated in terms of maximum and ultimate rotations. The comparison results between plastic rotation limits proposed by design codes and the test results indicate that AISC 341-16 is more suitable for the design of cold formed hollow sections with moderate heat treatment under this investigation, though the recommended reduction factor of axial load might be conservative.

Axial compressive behaviors of multi-cavity concrete-filled double-skin tubular stub columns

The axial compressive behaviors of multi-cavity concrete-filled double-skin steel tubular (MCFDST) stub columns are investigated using experimental and numerical methods in this study. The MCFDST columns comprise two concentric steel tubes (circular hollow section (CHS) inner and square hollow section (SHS) outer), sandwiched concrete filled between them, and four strips connecting outer and inner tubes. Fourteen MCFDST stub columns and two concrete-filled double-skin steel tubular (CFDST) (CHS inner and SHS outer) stub columns are fabricated and tested. Experimental results are used to validate the accuracy of finite element models of MCFDST and CFDST stub columns, and based on which, extensive parameter analyses are conducted. The analysis results show that the strips delay the local buckling and change the buckling mode of outer steel tube, as well as improve the bearing capacity and ductility of stub columns. Observed failure modes are controlled by the local buckling of the outer tube associated with the crushing of filled concrete. In addition, the axial compressive performance of MCFDST stub columns can be improved by reducing the width-to-thickness ratio of outer tube, increasing the steel yield strength of outer tube and concrete strength, and adding strips. The hollow ratio has a negligible effect on the axial compressive behaviors when it ranges from 0.26 to 0.56. Furthermore, the predicted results by European, Japanese, British, and Chinese codes are compared with the experimental and FE results, suggesting that the formula in the European code has the best accuracy when predicting the load-bearing capacity of MCFDST stub columns.

Experimental study on CFRP reinforcement and static performance of CHS KT-joints

Owing to the engineering application demands for the reinforcement of complex joints in multiplanar circular hollow section (CHS) trusses, this study investigated the reinforcement methods and static performance of KT-joints strengthened with carbon fibre-reinforced polymer (CFRP) sheets. First, CFRP reinforcement strategies for KT-joints were studied. Experimental comparisons in static performances were then conducted between bare and CFRP-strengthened CHS KT-joints. Meanwhile, CFRP reinforcement mechanisms were analysed. Finally, CFRP effective strain index η was proposed for quantitative assessment of CFRP strength utilisation. The results indicated that CFRP effectively restrained chord depression and expansion deformation, prevented local buckling of the compressive brace, and reduced strain concentration near the intersection lines. Compared with the bare joint, the ultimate load-bearing capacity and ductility of the joint reinforced with 4 layers of CFRP sheets on the chord and 3 layers on the braces increased by 24% and 25%, respectively. The initial stiffness of the joint at compressive and tensile brace locations increased by 48% and 375%, respectively. The η varied at different regions of the joint, with the maximum η found near the K-shaped gap and the intersection line of compressive brace. Based on the distribution of η, strategies for improving CFRP strength utilisation were proposed.

Experimental and numerical investigations of austenitic stainless steel semi-oval hollow sections under combined compression and bending

Semi-oval hollow section is an innovative cross-section profile, including one semi-circular flange, one flat flange and two flat webs. While the semi-circular flange (exposed to fluid or wind) offers a low level of hydrodynamic or aerodynamic drag, the flat elements facilitate connections with other members. This paper presents experimental and numerical investigations into the local buckling behaviour and resistances of austenitic stainless steel semi-oval hollow sections under combined compression and bending. A testing programme was firstly conducted and included initial local geometric imperfection measurements and ten eccentric compression tests. In conjunction with the testing programme, a numerical modelling programme was performed, where finite element models were developed to validate against the test results and conduct parametric studies for expanding the test data pool over a wider range of cross-section dimensions and loading combinations. The obtained test and numerical data were used to evaluate the applicability of the relevant design interaction curves for austenitic stainless steel rectangular hollow sections, as prescribed in the European code and American specification, to austenitic stainless steel semi-oval hollow sections. On the basis of the evaluation results, the codified design interaction curves were found to provide conservative resistance predictions. Finally, an improved design interaction curve, with more accurate end points and suitable shape, was developed and led to more accurate and consistent resistance predictions for austenitic stainless steel semi-oval hollow sections under combined compression and bending.

Sequence effects on the life estimation of welded tubular structures made of S355J2H under uniaxial fatigue loading

The use of hollow sections to form lightweight structures is widespread in common steel processing industries such as crane, commercial vehicle, steel bridge and agricultural machinery construction. The hollow sections are mainly designed as truss or frame structures, in some cases using high-strength and higher-strength steels in order to achieve optimum utilization of the component and material. A new collection of fatigue life data covering sequence effects and the accuracy of the linear damage accumulation is presented. Effects of the shape of the applied load spectra and sequence effects of different amplitudes have been investigated. This document covers tubes of 4 to 8 mm thickness made by low-carbon or mild steel S355J2H. In general, it was found that the spectrum shape and the loading sequence have an influence on the service life. Depending on the shape of the spectrum, random tests tended to lead to shorter service lives than tests with block-loading sequences. An influence of overloads was also found for the tests with interspersed overloads. Typical maximum linear damage sums taken from recommendations and codes of 0.2 or sometimes 0.5 are exceeded for all spectra investigated and in some of the cases even significantly above 1.0. Transferability of the recommendations to component-type structures like tubular joints needs revision to lift its lightweight potential. Using stress concentration factors (SCF) from finite element analysis, typical strength values for the structural and effective notch stress concepts are checked. All joints investigated show a significantly higher strength compared to the IIW recommendations using the structural stress approach or compared to the DVS 0905 with the effective notch stress approach.

Stability design of cold-formed high and ultra-high strength steel thin-walled box sections using effective stress-strain model

This paper proposes an effective stress-strain model for integrated analysis and design of cold-formed steel structures with thin-walled sections. The study focuses on square and rectangular hollow sections made from high and ultra-high strength steel. Initially, a shell-finite element model (SFEM) was developed and validated using experimental data, specifically for cold-formed members subjected to axial compression. Subsequently, a comprehensive parametric study is conducted to establish the stress-strain relationship model through nonlinear finite element analysis. The proposed model incorporates material nonlinearity, cold-forming effect, local plate imperfection, and residual stresses into a unified stress-strain curve, leading to advanced structural analysis and design of cold-formed structures using simple one-dimensional beam-column element. Subsequently, the proposed method is then implemented in the conventional finite beam-column element analysis, demonstrating consistent agreement with both experimental tests and sophisticated finite shell element results. Finally, the robustness and validation of the proposed method are established, and its application is exemplified through the design of a modular integrated construction (MiC) structure. This study highlights the versatility and reliability of the proposed approach for the analysis and design of cold-formed steel structures.

Early detection of steel tube welded joint failure using SPC-I nonlinear ultrasonic technique

Welding is a commonly used method for joining two or more parts together in steel construction. Various defects in weld regions such as cracks, pores, and slag inclusion can be present from the beginning, generated during the welding process, or can be developed while in service. Such defects are the weak spots that degrade the structure’s quality and can lead to structural failures. Therefore, early detection of these defects in welded joints, before visible cracks appear, is very important. Using appropriate ultrasonic non-destructive testing and evaluation (NDT&E) techniques, one can detect these defects and take remedial actions to prevent catastrophic structural failures. Guided acoustic wave-based techniques have been proven to be effective for damage detection in steel pipes and rods. Several studies have previously attempted to detect damage in steel tubes using guided ultrasonic waves. Unlike earlier attempts which mostly focused on conventional linear ultrasonic techniques, a relatively new nonlinear ultrasonic technique called sideband peak count-index (SPC-I) is carried out in this research. For this investigation, cast steel components and round hollow structural sections are welded together, and a four-point bending test is conducted under fatigue loading. The welded joints are continuously monitored in real time using strain gages and lead zirconate titanate (PZT) transducers. The PZT transducers are used to generate and receive guided acoustic waves. The signal is propagated through the specimen in a single-sided transmission mode setup. The strain gage readings and the nonlinear ultrasonic parameter, the SPC-I values, are monitored simultaneously. The results obtained from the nonlinear ultrasonic NDT&E measurements are compared with the data obtained from the strain gages to determine the robustness and reliability of the SPC-I technique for monitoring welded joints. This investigation also shows the potential effectiveness of the nonlinear ultrasonic parameter SPC-I for early detection of weld failure.

Flexural buckling of cold-formed austenitic stainless steel flat-oval hollow section columns: Testing, modelling and design

The flexural buckling behaviour and resistances of cold-formed austenitic stainless steel flat-oval hollow section columns are studied in this paper, based on experiments and numerical modelling. An experimental investigation was firstly conducted and included tensile coupon tests, initial geometric imperfection measurements and major-axis and minor-axis pin-ended compression tests on ten column specimens. The experimental investigation was followed by a numerical investigation, where the column test results were used to validate finite element models; upon validation, parametric studies were conducted to generate additional numerical data over a wide range of cross-section dimensions and member effective lengths. The obtained test and numerical data were adopted to assess the applicability of the relevant buckling curves for cold-formed austenitic stainless steel circular and elliptical hollow section columns, as specified in the European code, American specification and Australian/New Zealand standard, to cold-formed austenitic stainless steel flat-oval hollow section columns. It was revealed from the assessment results that the buckling curves of the European code and American specification led to overall accurate and consistent flexural buckling resistance predictions, while the flexural buckling resistance predictions from the buckling curve of the Australian/New Zealand standard were slightly conservative.

Flexural Strength of RHS Perforated Lean Duplex Stainless Steel Beam at Temperature 24-900ºC

The investigation of stainless steel structures at elevated temperatures is still limited, especially to those focused on the behaviour of perforated beams. Therefore, a numerical study was conducted to investigate the behaviour and strength of cold-formed lean duplex stainless steel (CFLDSS) beams having a single web perforation that failed due to pure bending at temperatures between 24-900oC. In total, 200 square and rectangular hollow sections (RHSs), which had various cross-section sizes, hole diameters, and temperature simulations, were involved in the parametric study. The numerical study was based on the ABAQUS simulation results of the 200 specimens. The numerical model was developed based on the validated existing studies. Numerical evaluations show that the existing codified strength predictions are conservative, but it has inconsistent safety. Hence, this study suggests modifications to the existing strength prediction, which is more conservative and reliable.

Fatigue strength of single-sided fillet welds in overlapping ultra-high-strength steel sheets

From the manufacturing viewpoint, overlapping thin sheets can provide a substantial geometrical improvement in welded hollow sections compared to butt-welded cross-sectional details. However, the plate eccentricity and non-penetrating fillet welds make the joints susceptible to fatigue failures under transversal cyclic loads. This work experimentally investigates the fatigue strength of overlap joints prepared with gas metal arc welding in the single-sided fillet weld configuration. Fatigue tests were carried out on the lap joints made of S960 ultra-high-strength steel (UHSS) grade under uniaxial constant amplitude axial loading employing both pulsating tension (applied stress ratio of R ≈ 0) and pulsating compression (R ≈ -∞). In addition, the lap joints were prepared with both straight welds (the welds transverse to the loading direction) and inclined welds (the welds with a 30° inclement angle from the transversal direction) to investigate the shear stress effects on the joints’ fatigue performance. Plasma butt-welded samples were tested as a reference join type. For the plasma butt-welded joints, the recommended detail category of FAT71 in the nominal stress system for weld root failures in single-sided butt welds was observed clearly conservative—a mean fatigue strength of Δσc,50% = 130 MPa with a fixed slope parameter of m = 3 was obtained. Compared to the butt-welded joints, a significant decrease in fatigue strength capacity was found in the lap joint specimens with misalignment factors of km > 3.0. The failure locations were also different in joints subjected to the tension and compression loads. The shear load did not majorly contribute to the changes in the fatigue strength capacity compared to the joints subjected to the transversal normal stress.

Experimental study of concrete-filled stainless steel tubular stub columns with circular and square cross-sections subjected to combined compression and bending

This paper presents an experimental study into the structural behaviour and strength of concrete-filled stainless steel tubular stub columns with circular and square cross-sections subjected to combined compression and bending moment. A total of sixteen concrete-filled stainless steel tubular (CFSST) stub columns were tested, including two section types (circular and square hollow sections), two grades of concrete infill (C30 and C60), two thicknesses of tube wall for each cross-section (6 and 10 mm), and five loading eccentricity ratios (0, 0.2, 0.3, 0.4 and 0.5). The CFSST stub column specimens were loaded in compression, with different loading eccentricities applied to achieve a wide range of axial load-to-bending moment ratios. This research provides a comprehensive report on the experimental methodology and subsequent observations, including the failure modes, load-deformation curves, axial load-bending moment curves, strain development at the key locations and values of ductility index. It can be observed that for circular CFSST columns, ultimate load decreased by roughly 70% with an increase in loading eccentricity ratios from 0 to 0.5, while for square columns, the reduction was about 50% under same conditions. The experimental results were used to evaluate if the existing design provisions for carbon steel-concrete composite structures is capable of designing the investigated CFSST stub columns. It was found that the mean ultimate load to predicted failure load ratios are 1.25, 1.32, and 1.36, with coefficients of variations (COV) equal to 0.08, 0.09 and 0.11, for the European, American, and Chinese codes, respectively. Consequently, the design approach specified in the Chinese code led to the most conservative and scattered strength predictions among the three codified design approaches. In contrast, the European code provides the most precise predictions of the test results, though there still remains scope for improvements in the ultimate resistance predictions of CFSST stub columns subjected to combined compression and bending.

Method and experimental study of strengthening circular hollow section T-joints by partial filling with cementitious materials

Circular hollow section truss joints may need to be strengthened for various reasons. This study evaluated a new method for strengthening such joints by partially filling the chords with cementitious materials, including grout and mortar. Taking T-joints as an example, the proposed strengthening process was described and experiments were conducted on six joints (four strengthened and two unstrengthened) under axial compression or tension applied to the braces. The failure modes and structural behaviors of the joints before and after strengthening were compared, and the effects of the strengthened length, filling material, direction of brace loading, and presence of temporary openings in the chord on the performance of the T-joints were investigated. The results demonstrated that: the strengthening method was viable and effective, the T-joint filled with 1d0 grout (mortar) exhibited a 70% (33%) improvement in initial stiffness and a 50% (36%) improvement in ultimate loading capacity; the use of grout was more efficient and convenient for construction than mortar; the initial stiffness and ultimate loading capacity of the strengthened T-joint was also improved when the brace were under tension; the temporary openings cut in the chord during the strengthening process had a little effect on the performance of the T-joint, with reductions of 11% and 9% in initial stiffness and ultimate loading capacity, respectively. Thus, the performance and safety of the joints can be ensured if reasonable design and protection measures are implemented.

Flexural behaviors of a novel precast hollow UHPC composite beam reinforced with inverted T-shaped steel: Experimental investigation and theoretical analysis

To fully utilize the excellent mechanical properties and durability of ultra-high performance concrete (UHPC) as well as reduce the production cost, a novel UHPC encasing inverted T-steel (PUES) composite beam with hollow section is proposed in this paper. This paper aims to study the flexural behaviors of PUES beams, a bending test program consisted of one solid PUES beam and seven hollow PUES beams is carried out. The test parameters include thickness of inverted T-shape steel flange, tensile reinforcement ratio and stud spacing. The results showed that the PUES beams failed in the typical flexural failure mode and exhibited excellent ductility without obvious drop in load. Compared to composite beam with solid section, the hollow section had negligible influence on the flexural performance of PUES beams, while it saved 26 % UHPC used compared with the one with solid section. The increasing of the thickness of inverted T-shape steel flange and the reinforcement ratio effectively improved the stiffness and the flexural capacity of PUES beams, while the larger diameter of reinforcement incurred an obvious reduction of ductility. An excessively large stud spacing resulted in a poor composite behavior and a reduction of flexural capacity. Based on the analysis of the experimental results, calculating methods considering the shear connection degree between inverted T-steel and peripheral reinforced UHPC were developed to predict the ultimate flexural capacity of the hollow PUES beams. This study provides a reference for further research and practical engineering applications of this innovation composite beam.

Residual stresses of MAG-welded ultrahigh-strength steel rectangular hollow sections

Residual stresses are an important factor in the performance and stability of welded structures. This study investigates the characteristics and significance of residual stresses in MAG-welded ultrahigh-strength steel rectangular hollow sections. The research incorporates comprehensive X-ray diffraction residual stress measurements, electron backscatter diffraction analysis, statistical analyses, and finite element method simulations to provide valuable insights into the behaviour of welding residual stresses. The results reveal clear microstructural variations between the cold-formed corner and the flat side of the rectangular hollow section caused by welding heat input, emphasizing the need to consider these variations in residual stress assessments. Furthermore, the study examines the dependence of residual stresses on the steel grade, with higher strength steel exhibiting compressive stresses and lower strength materials experiencing tensile stresses in corner areas. Statistical analysis indicates that welding sequence and direction have negligible effects when applying the employed welding sequence. In any case, higher heat input leads to significantly larger residual stresses. Finally, the study presents a novel analytical model based on validated finite element simulations to predict the maximum variation of residual stresses depending on welding heat input. The findings provide valuable insights into the significance of welding residual stresses and their predictability. The comprehensive measurements, simulations and proposed models contributes to a better understanding of residual stress phenomena, facilitating the development of reliable design guidelines for welded structures in various engineering applications.

Low-high-low cyclic performance of screw connections for fibre-polymer composites

This study examines the cyclic performance of screw connections for joining fibre polymer composite members. Cyclic tensile experiments were conducted on connection specimens consisting of a flat panel (FP) and a square hollow section (SHS) at a right angle. A low-high-low (LHL) cyclic loading program was employed, consisting of seven varying-amplitude loading sequences spanning over 10,361 cycles, in order to simulate wind actions according to relevant standards. Four types of specimens, connected using screws or/and adhesive bonding, were examined, under three load amplitude levels corresponding to 50%, 80%, or 100% of the monotonic ultimate load. All specimens loaded under the LHL amplitude levels of 50% and 80% of the monotonic ultimate load survived after all LHL cycles. These survived specimens were subsequently loaded to determine their retention capacity. The results revealed that no less than 89% of the monotonic strength was preserved. In the LHL loading process, the specimens with adhesive bonding showed more severe degradation of stiffness than their screw-only counterparts, due to the initiation of delamination near the bonded side edges on the FP in the early stage of cycles, with further propagation as the number of cycles increased. The screw-only specimens also demonstrated comparable retention capacity in comparison to the adhesively-bonded specimens.

Eurocode-compliant system-level reliability analyses of trussed portal frames under climatic loads

Eurocode 3 provides Geometrically and Materially Nonlinear Analysis with Imperfections-method (GMNIA) in which the entire structure can be designed in system-level. In GMNIA, reliability of structural system is verified by using a system safety factor which is obtained in Eurocode 3 based on numerical or experimental capacity test results. Unfortunately, such test results are scarcely published in the literature thus complicating the determination of the factor for a design engineer. In the so-called Direct Design Method, however, system safety factors are provided in advance for the design engineer by system-level reliability studies. This study determines the Eurocode-compliant GMNIA system safety factor for Warren truss portal frames by using the approach of the Direct Design Method. Advanced numerical models are utilized to perform Monte Carlo-simulations for entire structural systems. These simulations provide statistical distributions of system resistances which are employed in the First-Order Reliability Method to derive the system safety factors. Studied structures are made of S700 cold-formed hollow sections. Various system geometries, system configurations and load combinations consisting of snow and wind loads are investigated and a suitable system safety factor is proposed for the ultimate limit state design of Warren truss portal frames. The proposed system safety factor is applied in a practical comparison in which Warren system is designed both by the conventional Eurocode 3 method and GMNIA. This comparison reveals that GMNIA has a remarkable potential to offer reduced material consumption in design compared to the conventional method.

Numerical analysis and design methods of grout-filled GFRP tube repaired corroded CHS T-joints

This study explores the compressive behavior of Grout-Filled GFRP Tube (GFGT) repaired corroded circular hollow section (CHS) T-joints. Finite element models of GFGT repaired corroded joints were developed, validated, and utilized to examine the influence of the joint geometric, material, and chord end stress parameters on the compressive strength and repairing efficiency of the joints. The findings reveal that the ultimate strength of the GFGT repaired joint increases with a thicker GFRP tube, a lower repaired chord section hollow ratio, a higher grout strength, and a longer repaired range. By optimizing the repairing parameters of the grout-filled GFRP tube, the compressive strength of GFGT repaired corroded joints with 16% and 32% corrosion rates can be up to increase to 164% and 147% of the uncorroded counterparts, respectively. The chord end stress exerts a similar but weaker effect on the repaired joints than on the unrepaired joints. A series of suggestions were proposed for repairing joints with different corrosion degrees to achieve a 20% ultimate strength enhancement compared to uncorroded joints. The compressive strength degradation rate of corroded joints was accurately predicted by the design method in the CIDECT and prEN guidelines. The feasibility of the guideline formulae to evaluate the strength reduction rate caused by the chord end preload was verified. A design method to predict the compressive strength of GFGT repaired corroded joints was proposed.

Web crippling tests of cold-formed stainless steel tubular sections at elevated temperatures

This paper presents an experimental investigation on web crippling behaviour of cold-formed stainless steel square and rectangular hollow sections (SHS and RHS) at elevated temperatures. A total of 21 web crippling tests were conducted under the Interior Two-Flange (ITF) loading condition as codified in ASCE/SEI 8–22 Specification at various temperatures up to 800 °C. Tensile flat and corner coupon tests were conducted to obtain the material properties of the cold-formed stainless steel SHS and RHS at various temperatures corresponding to those pre-set in the web crippling tests. Details of the test specimens, setups and procedures are comprehensively documented in this paper. Furthermore, the specimen temperatures together with the test results, including failure modes, web crippling strengths and load-deformation curves are fully reported. The obtained test results were used to evaluate the suitability of codified web crippling design provision as per ASCE/SEI 8–22, where reduced material properties were used in calculating the web crippling strengths at elevated temperatures. In addition, the test results were also compared with the predictions obtained from existing design rules in literatures for cold-formed stainless steel SHS and RHS at elevated temperatures. Moreover, reliability analyses were conducted to assess the reliability levels of these design provisions. It is demonstrated that the available web crippling design provisions can provide generally conservative and reliable strength predictions, and therefore are deemed suitable for predicting the web crippling strengths of cold-formed stainless steel SHS and RHS at elevated temperatures.

Industrial Building Structure Planning With Cranes

Industrial building structure planning complies with standards and regulations, such as Procedures for Earthquake Resistance Planning, Minimum Loads for Building Design, and Specifications for Structural Steel Buildings. Vertical and lateral loads are fundamental to the structure's load flow process. Industrial buildings handle roof, wind, earthquakes, crane, and wall loads. Structural design must consider these elements, including the choice of lateral force-resisting systems such as X-bracing. In determining building loads, including earthquake and wind loads, various parameters such as wind speed, exposure category, and other factors must be considered by standard requirements such as SNI 1727-2020 and SNI 1726:2019. Selection of site class, wind direction, topographic, and ground surface elevation factors are essential in determining wind loads. This research method focuses on supporting structures consisting of purlins and girts in the context of industrial buildings. Purlins, made from hot or cold rolled steel, generally use C and Z profiles. Girts, made from cold or hot rolled steel, have profile variations such as C, Z, or hollow square sections. The girt structure design process determines dimensions, rod sag, internal requirements, and sag rod capacity.