Hysteretic Energy Dissipation Capacity Research Articles

Development and tests of novel repairable multi-stage yielding steel slit dampers for seismic mitigation

This paper develops a novel repairable multi-stage yielding steel slit damper (denoted as RMYD) for seismic mitigations of engineering structures. The configuration and desired nonlinear behavior of RMYDs were first presented. Then, 7 specimens were designed to investigate the hysteretic performance of the proposed RMYD under cyclic loading, and the effects of design parameters of the RMYD and the loading protocols were studied through parametric tests. The experimental results show that the RMYD specimens can obtain the desired multi-stage yield behavior with stable hysteretic responses and excellent ductilities under cyclic loading. The repaired RMYD specimen can show the nearly same hysteretic responses as the original one, confirming the excellent repairability of the proposed RMYD. Moreover, the RMYD specimen under near-fault loading protocols shows stable multi-stage hysteretic responses, demonstrating the reliable damage-control and hysteretic energy-dissipation capacities under near-fault earthquakes. Finally, the design recommendations were provided for practical applications. The excellent ductility, multi-stage yield capacity, hysteretic energy-dissipation capacity, and post-earthquake repairability make the proposed RMYD a promising and practical damper for seismic mitigation of engineering structures.

Energy dissipation evaluation of butterfly-shaped steel plate shear keys under different loading protocols

This paper proposes a novel energy dissipation shear key (ED shear key) for small-to-medium-span highway bridges using butterfly-shaped steel plates for enhanced energy dissipation capacity. Reversed cyclic loading tests were conducted on two series of specimens which had different designs of structural dimensions. Four distinctive loading protocols were adopted to allow an in-depth examination of the seismic hysteretic behavior and energy dissipation capacity of the ED shear keys. The test results reveal that the ED shear keys exhibited distinctive characteristics before and after buckling of steel plates. The recorded force-displacement curves of the ED shear keys were plump before buckling and typically became pinched after buckling. The loading protocol had a significant effect on the energy dissipation of the ED shear key specimens, with an over 90% increase in energy dissipation observed under the constant-amplitude loading protocol compared to the incremental-amplitude ones. It was found from the test results that the profile of the force-displacement skeleton curves was hardly affected by the loading protocols, as a result a trilinear skeleton model is developed to characterize the force-displacement relationship of the ED shear keys. Furthermore, by decomposing the force-displacement hysteresis curve into a skeleton part and a Bauschinger part, an evaluation model is established for predicting the energy dissipation capacity of the ED shear keys. Validation against the test results indicates that the evaluation model can provide a satisfactory accuracy for predicting the energy dissipation of the ED shear keys subjected to various loading protocols.

Experimental Study on Energy Dissipation Performance of SPA Shear Plate Metal Damper Based on Jacket Platform

Aiming at the problem of excessive vertical vibration caused by seismic primary waves in jacket structures located in seismic zones in China, a new type of shear plate metal damper with upper and lower elliptical openings (SPA) is proposed in this paper. The seismic model test is carried out to compare the shear plate metal damper with three traditional opening forms, central elliptical opening, single row opening, and double row opening, and the hysteretic curve, skeleton curve, and cyclic hysteretic energy dissipation capacity are analyzed. The results show that the energy dissipation performance of the new shear plate metal damper with upper and lower elliptical openings proposed in this paper is better than that of the other three types of dampers.

Seismic performance of novel low-damage stair system: Precast reinforced concrete stair isolated with a sliding joint

This research presents a solution that can solve the negative diagonal support effect of the traditional precast reinforced concrete stair with rigid connection (TS) and adverse stress centralization on the fragile reinforced concrete (RC) flight. This innovative low-damage stair system utilizes a sliding joint at the bottom of the precast RC stair (SS). Experimental and numerical investigations were implemented on specimens TS and SS to systematically evaluate the seismic responses of the presented low-damage stair system. Experiment results confirm that specimen SS could effectively eliminate the detrimental diagonal support effect of conventional stair systems and the unexpected overlarge stress concentration of the RC components. Therefore, the RC flight and landing beam of the proposed low-damage stair systems remained undamaged at the inter-story drift ratio up to the final level of 4.00%. Taking advantage of the sliding joint, specimen SS behaves with excellent hysteretic performance and energy dissipation capacity. Furthermore, parametric analysis results reveal that the concrete strength remarkably affects the seismic responses of the innovative stairs, while the impact of the friction factor of the sliding joint on the seismic performance is asymmetric during positive and negative loadings.

Hysteretic energy dissipation capacity of dual-steel welded-plate preloaded bolted T-stubs

With the high- and ultrahigh-strength steels applied in the construction industry, the seismic safety of their structural components is very concerned due to the inferior material ductility of those steels. The current studies on bolted high-strength steel T-stubs mainly focus on their monotonic loading behavior. There is limited research work conducted to study their cyclic loading behavior. In this study, cyclic tests of bolted dual-steel T-stubs were conducted. Their T-elements were produced by Q690 high-strength steel flanges and Q355 normal-strength steel webs, and class 10.9 high-strength bolts with pretension were used to connect the groove-welded T-elements. Failure modes, force-deformation hysteretic and backbone curves, cumulative plastic deformation and energy dissipation capacities were tested and analyzed. The test results indicated that an optimal β ratio between the plastic resistances of Mode 1 (neglecting the influence of bolt action on a finite contact area) and Mode 3 in Eurocode 3 Part 1–8, could be 0.3 for those bolted T-stubs to maximize hysteretic energy dissipation. Accordingly, predictive formulas with good precision were proposed for the low-cycle fatigue failure criterion and hysteretic energy dissipation capacity of those bolted T-stubs, respectively.

Cyclic behavior of lightweight engineered cementitious composite beam-column joints

This study investigated the behavior of exterior beam-column joints made of engineered cementitious composites (ECC) with varying densities (i.e., ranging from 1740 to 2080 kg/m3) under reversed cyclic loading. In total, six ECC joints were cast using different mixtures detailed as: (a) two normal weight ECC (NWECC) mixtures developed with silica sand (SS) as a filler and either polyvinyl alcohol (PVA) fibers or polypropylene (PP) fibers; (b) two lightweight ECC (LWECC) mixtures developed with lightweight slate sand (SL) as a filler and either PVA fibers or PP fibers; (c) one LWECC mixture developed with PVA fibers and the filler consisting of a combination of SL and powder rubber (PR) in a ratio of 70%:30% (by volume); and (d) one LWECC mixture developed with PVA fibers and the filler consisting of a combination of SL and crumb rubber (CR) in a ratio of 70%:30% (by volume). An additional joint made of conventional lightweight concrete (LWC) with a density of 1850 kg/m3, was tested for comparison. The steel reinforcement details were kept the same on all specimens conforming to the typical design of strong column-weak beam concept. The hysteretic behavior, capacity, stiffness, cracking behavior, ductility, and energy dissipation capacity of all tested joints were assessed. The results indicated that utilizing SL alone helped to successfully develop lightweight joints with a mixture density of less than 1850 kg/m3 and strength-to-weight ratios comparable to those of NWECC. However, these joints exhibited lower ductility and energy dissipation capacity compared to NWECC joints. Using PR or CR with SL appeared to be a more efficient alternative over using SL alone, in constructing LWECC joints with lighter self-weight, higher ductility, and higher energy dissipation capacity. Notably, all LWECC joints demonstrated superior structural performance compared to the LWC joint, even though they were lighter, thus indicating promising potentials of LWECCs for lightweight structures. The results also revealed that in all tested specimens, the PVA fibers exhibited better performance over those with the PP fibers.

Seismic performance of circular concrete-filled steel tube columns reinforced with inner latticed steel angles

The seismic behavior of circular concrete-filled steel tube (CFST) columns with inner latticed steel angles under combined axial load and reversed cyclic horizontal load was studied in this paper. A total of 8 specimens was tested, including two CFST specimens and six latticed steel angles reinforced CFST specimens. The main parameters studied were the diameter-to-thickness ratio of steel tube, the cross-sectional area of inner latticed steel angles and the axial compression ratio. Firstly, the load-displacement curves and load-strain curves were obtained experimentally; secondly, the failure modes, hysteretic behavior, skeleton curves, stiffness degradation, ductility index, hysteretic energy dissipation capacity were analyzed; thirdly, the seismic performance of the tested specimens were simulated by the established finite element (FE) models, and parametric studies were subsequently performed; finally, the modified calculation method for the horizontal bearing capacity was proposed. The research results showed that the failure of the composite columns was caused by the local buckling of the latticed steel angles and steel tube, and the latticed steel angles could effectively participate in the overall loading process. It was also found that latticed steel angles are able to improve the energy dissipation capacity.

Seismic behaviour of Concrete-filled steel tubular column to H-Shape steel beam connection with side plate

To ensure the quality of filled concrete and improve the indoor utilization rate of steel frame structure residential buildings, a novel concrete-filled steel tubular (CFST) column to H-shape steel beam connection with side plate was proposed in this study. Six specimens of 1/3 scale were tested under reversed cyclic loading. To evaluate the hysteretic performance, failure mode, ductility, stiffness degradation, strength degradation and energy dissipation capacity. The evaluation parameters include the axial load ratio, and the side plate height and thickness. The results indicated that the failure mode mainly exhibited the steel beam buckling failure, making all hysteretic curves exhibit typically spindle-shaped. The equivalent viscous damping coefficient is 0.305–0.394. The average story drift angle at the ultimate stage is 1/31 ∼ 1/37. It shows that all connections possess sufficient energy dissipation capacity and excellent ductility. The peak and ultimate load are significantly reduced with the increase of the axial load ratio. And the secant stiffness increases in the elastic stage with the rise of the thickness and height of the side plate. Finally, the failure mode, hysteresis curve, and envelope curve achieved from the finite element method(FEM) established in this paper are consistent with the test results. And the FEM disclosed that the beam flange stress is transferred to the side plate through the fillet weld, and the side plate stress is transferred to the column panel through the fillet weld.

Performance of box-shaped column connection achieved with local grouting and bolts

To prevent the traditional box-shaped column flange connection from affecting the facade of the overall structure, this study proposed a box-shaped column connection achieved by local grouting and bolts. One integral box-shaped column specimen and two box-shaped column connection specimens were designed. The seismic performance of the connection and the influence of local grouting on the mechanical performance of the connection were studied. The failure phenomenon of the specimen was observed, and the mechanical performance of specimens, such as hysteretic behavior, bearing capacity, stiffness degradation, ductility, and energy dissipation capacity were examined. Results are as follows: the failure mode of the integral box-shaped column specimen and the specimen connected by local grouting and bolts is plastic hinge failure; the effect of local grouting can improve the integrity of the connection and obtain good energy dissipation capacity; the effect of local grouting can increase the bearing capacity of specimen by 24.84% and reduce the bolt tensile force by 34.37%; the steel connector at the column–column joint prevented the buckling deformation of the box-shaped column; the ductility is increased by 22.06%; no slip occurred between the upper and lower steel connector. Therefore, the new joint is safe and reliable. Through numerical simulation analysis, the research results show that the joint can be equivalent to rigid connection. The peak bearing capacity of the box–column joint is checked according to the Code for Seismic Design of Buildings: GB50011–2010. The calculation results are consistent with the experiment results.

Experimental investigation of the behavior of traditional timber mortise-tenon T-joints under monotonic and cyclic loading

• Monotonic & cyclic tests on traditional cylindrical mortise-tenon timber T -joints. • Great displacement capacity but also severe pinching in hysteresis loops. • Significant difference in force capacity if tenon under shear or bending. • Behavior also influenced by inherent material variations, construction etc. Monotonic and cyclic tests on cylindrical mortise-tenon timber T-joints typical of Ottoman-period mansions in mainland Greece were carried out, aiming towards a better understanding of such connections and their influence on timber-framed wall seismic performance in numerical and experimental investigations. Configurations from the head and foot of posts were tested so that the tenon was under either combined bending and shear, or pure shear. The two types of loads led to significantly different hysteretic behavior, force and energy dissipation capacity of the examined joints. Joints with gap and under push–pull out load were also tested.

Effects of gaps on the seismic performance of traditional timber frames with straight mortise-tenon joint: Experimental tests, energy dissipation mechanism and hysteretic model

The gaps are very common in the mortise-tenon (M-T) joints of the column-frame layer for the existing ancient timber buildings, which severely threaten the whole stability and safety of the structures. To study the effects of gaps on the seismic performance of traditional timber frames with straight M-T joint. Three 1/3.2-scaled straight M-T jointed timber frames, including one intact timber frame as a contrast and two timber frames with different gaps, were fabricated using Pinus sylvestris logs, and subjected them to reversed cyclic loading tests in strict accordance with the international test standard ISO-16670. The failure modes, load-displacement hysteretic response, strength, initial elastic stiffness, ductility, and stiffness degradation of the specimens were analyzed. The energy dissipation mechanisms of the timber frames with different gaps were evaluated, based on the law of energy conservation. Results indicated that the strength, initial elastic stiffness, and hysteretic energy dissipation capacity of the timber frames with gaps decreased significantly with increasing damaged degree. The gap can weaken the ductility of the timber frame, however, the inter-story drift ratio of the timber frame with gap can reached 0.16, indicating good deformation capacity. The gap had little effect on the degradation degree of the residual stiffness of the timber frame under large displacement amplitude. When the damage degree was 10%, under large displacement amplitude, the hysteretic energy consumption, elastic strain energy, and gravitational potential energy of the timber frame approximately accounted for 54%, 16%, and 30% of the total input energy, respectively. Based on the experimental results, the empirical formulas related to key cyclic performance parameters, considering the gap effects, were established. Based on the empirical relationships of the key hysteretic parameters of the timber frame with gaps, an improved hysteretic model for a timber frame with a gap was proposed and also validated. Good agreement between the model predictions and experimental results was observed.

Hysteretic behavior of a new type of outsourcing hybrid joint

The joints of the upper and lower structures are the key to ensure the overall cooperative capacity of reinforced concrete frame-added layer hybrid structure. A new type of outsourcing joint and a new type of outsourcing reinforced joint for the hybrid structure were proposed in this study, which were used to effectively alleviate the stiffness mutation and enhance the column foot constraints on the upper structure. The quasi-static experimental and finite element nonlinear numerical analysis results of new joints and exposed rigid joint were carried out. The anti-seismic performance of its hysteretic curves, skeleton curves, strength degradation, stiffness degradation and energy dissipation capacity were compared and analyzed. Results indicate that the three specimens are all beam hinge failures. The hysteretic curve of new type outsourcing reinforced joint is plump, and the plastic hinge is moved outwards, which protect the core area of the joint effectively. Its stiffness degradation, equivalent viscous damping coefficient, energy dissipation capacity and other indicators are improved to different degrees compared with the new type of outsourcing joint and exposed rigid joint. Thus, the new type of outsourcing reinforced joint has a higher load-bearing capacity and stiffness, and better seismic performance. This study can provide scientific basis and technical support for the popularization and application of steel structure-added layer hybrid structure.

Analysis of the Seismic Behavior of a Wall Pier of a Covered Bridge Based on the Multi-Layer Shell Element

To investigate the seismic behavior of the wall pier of a covered bridge, the multi-layer shell element in OpenSEES was used to carry out the numerical analysis under a horizontal low cyclic loading in the weak axis direction. The effects of the mesh divisions of the wall pier models were evaluated and the hysteretic curves, skeleton curves, bearing and energy dissipation capacity, stiffness degradation and displacement ductility of the wall pier with different lateral loading modes were mainly researched. The results demonstrate that the discretization of layers along the thickness direction of the multi-layer shell element model has a very limited effect on the hysteretic and skeleton curves. The mesh division of the horizontal direction depends on that of the vertical, and the vertical mesh spacing shall be longer than the plastic hinge with a length of 0.5744 m. The arrangement of the loading points is critical for the seismic behavior of the wall pier. The pier suffering the force from the five points presents a relatively strong energy dissipation and larger ductility, but this layout may cause a more concentrated force at the local position. When the loading points are evenly distributed, the capacity and displacement changes sharply and the ductility diminishes. Successively, the seismic performance indexes at the local position of the wall pier tend to be more consistent with the increasing loading points. The deformation and energy dissipation capacity of the nearby position with the denser side loading points becomes larger, but this has a minor impact on the seismic performance of the position far from the points. The wall pier without the bent cap and with three bearings set is supposed to be more reasonable for the covered bridge through the overall analysis of seismic performance.

A partially restrained energy dissipater: Parametric analysis and application in rocking wall

To solve the limitations of the large-scale buckling-restrained brace and expand its application in rocking structures, a partially restrained energy dissipater (PRED) was developed recently. The partially restrained mechanism and the hysteretic behavior of PREDs have been verified by tests, whereas systematic studies of the PRED considering various design parameters have not yet been formed. In this study, parametric analyses of the PRED based on five series of numerical cases were conducted, which aimed at comprehensively studying the effect of the out-of-plane gap, length and number of the yielding segments, edge chamfering and thicknesses of the restraining tube on the seismic performance of the PRED and providing design recommendations. It is determined that the equivalent viscous damping ratio and compression-strength adjustment factor of the PRED decreased with the increasing out-of-plane gap. The overall hysteretic behavior and energy dissipation capacity were almost not affected by the number of yielding segments and their length. The thickness of the restraining tube should be equal to 4 mm or larger to avoid local plasticity. A detailed design procedure for PREDs was established based on the numerical analyses. Finally, PREDs were applied in a previously tested cross-laminated bamboo (CLB) rocking wall numerically to investigate the effectiveness of the PRED in rocking structures. The results showed that the energy dissipation and stiffness of the CLB rocking wall can be significantly improved by PREDs. This study lays a foundation for the application of the PRED in actual rocking structures and promotes the development of high-rise bamboo structures.

Experimental study on seismic performance of prefabricated viscoelastic damping bolted joints

Aiming at the defect of insufficient bearing capacity of prefabricated concrete beam-column joint with bolted connection, a prefabricated viscoelastic damping bolted joint (VDBJ) is proposed with good seismic performance. The damping principle is based on that viscoelastic (VE) dampers can provide energy dissipation and additional stiffness for the structures. Three full-scale beam-column joint specimens were designed, including one cast-in-place joint specimen, one prefabricated bolted joint specimen without VE dampers and one prefabricated bolted joint specimen with VE dampers. Since the viscoelastic damper is a passive energy dissipation device with velocity correlation, comparison and analysis of three specimens under high-frequency cyclic loading are performed on the failure modes and seismic performance indexes such as hysteretic energy dissipation, displacement ductility, stiffness degradation and ultimate bearing capacity. The analysis of the test results indicate that the proposed prefabricated viscoelastic damping bolted joint has stronger ultimate bearing capacity and displacement ductility than the cast-in-place joint. The arrangement of VE dampers effectively controls the appearance and expansion of concrete cracks, which not only achieves the expected effect of shock absorption and energy dissipation, but also can realizes the rapid replacement of components after the earthquakes.

Cyclic flexural performance of RC beams with small circular openings in plastic hinge region

This paper describes the effect of a small circular web opening located in the plastic hinge region on the cyclic flexural performance of RC beams. The variable in the design of specimens is the diameter of the circular web openings installed in the plastic hinge region. Two rectangular beams scaled down to 67% of a practical RC beam were fabricated to have circular openings in the plastic hinge region with diameters 0.2 and 0.3 times the height of the beam. In another beam, in addition to the opening in the plastic hinge region, a web opening with a diameter of 0.3 times the height of the beam was installed at a location 180 mm from the center of the span. A total of four beams including a control beam were subjected to cyclic anti-symmetric moment. The cyclic flexural performance of the beams was evaluated in terms of hysteretic response, including strength, stiffness, ductility, and energy dissipation capacity. The neutral axis depth of the plastic hinge during the cyclic loading test was calculated using the linear distribution of strains of longitudinal reinforcing bars placed at the top and bottom of the openings. In addition, using the effective depth of the RC beams and the net tensile strain in the extreme tension reinforcement for tension-controlled sections, which are recommended by ACI 318–19, the maximum diameter of the circular web opening in the plastic hinge region was approximated and compared with the test results. Furthermore, with reference to the results of certain exiting studies, the ratio of the spacing between openings to the maximum diameter of the circular web opening was suggested by assuming the case of designing web openings to leap over major shear cracks expected to occur in a flexural RC beam undergoing shear-flexural failure.

Study on seismic performance of welding beam reinforced with symmetrical flange plate to H-shaped column after fire

The objective of this paper is to investigate the seismic performance of welding beam strengthened with symmetrical flange plates to H-type column (WBSFPHC) after fire. The accuracy effectiveness of the calculation model was verified using the existing experimental results. Considering the application of practical engineering parameters, the column width-thickness ratio (α), ratio of beam width to column width (β), height-thickness ratio of beam web (γ), width-thickness ratio of stiffener (ε), length thickness ratio of flange plate (η) and temperature (T) were used to perform a parametric study against the post-fire seismic performance of the WBSFPHC connections. Then, 25 calculation models were established to explore hysteretic behavior, stiffness degradation, ductility and energy dissipation capacity of the WBSFPHC connection under post-fire cyclic load. The results showed that the stiffness and bearing capacity of the WBSFPHC connection were improved with the increase of the parameters β and γ, temperature had great effect on the stiffness, stress distribution, energy dissipation capacity and bearing capacity of the WBSFPHC connection. The findings can provide reference and technical support to the seismic performance design, maintenance and reinforcement of such joints after fire.

Seismic retrofit of large-scale interior RC beam-column-slab joints after standard fire using steel haunch system

Steel haunch system was proposed to retrofit fire-damaged reinforced concrete (RC) beam-column-slab joints and ensure their seismic safety. Five RC beam-column-slab joints were designed, including one control specimen without fire damage, one control fire-damaged specimen, three fire-damaged specimens retrofitted with different types of steel haunch system, i.e., separate steel haunches, a combination of steel haunches and carbon fiber-reinforced polymer (CFRP) sheets, and a combination of steel haunches and bolted side plates (BSP). The fire-damaged RC joints were subjected to ISO 834 standard fire. After fire tests, low-cycle reversed loading tests were conducted on all the control and retrofitted specimens. The influence of fire damage and retrofit methods on the hysteretic behavior, load capacity, stiffness, ductility factor, and energy dissipation capacity of the joints was analyzed. Experimental results showed that fire exposure significantly reduced the seismic performance of RC beam-column-slab joints. The plastic hinges of spatial joints were transferred from the beam-column interface to the zone outside steel haunches after retrofitting. Compared with the control fire-damaged specimen, the hysteretic curves of the retrofitted specimens were more stable and plumper. All the three strengthening methods effectively enhanced the ultimate load capacity (increased by 24–70%), stiffness, ductility and cumulative hysteresis energy (increased by 107–362%) of the post-fire joints. CFRP sheets and bolted side plates show excellent compatibility with the steel haunches. The preload degradation of bolts used to fix the steel haunches reduced the retrofit efficiency of the steel haunch system. The numerical results of the sequentially coupled thermal-stress analysis model for retrofitted post-fire RC joints based on ABAQUS were consistent with the experimental results.

Seismic performance of prefabricated middle frame composed of special-shaped columns with built-in lattice concrete-filled circular steel pipes

Prefabricated buildings are green and environment-friendly, with high construction efficiency. Concrete-filled steel pipe structures have high bearing capacity and strong deformation ability. Special-shaped column frame structures of prefabricated concrete-filled circular steel pipe with built-in lattice can give full play to the advantages of prefabricated buildings and concrete-filled steel pipe structures, with the advantage of high space utilization rate of special-shaped column structures. In order to study Seismic performance of frame in special-shaped columns of prefabricated concrete-filled circular steel pipe with built-in lattice, a full-scale middle frame model specimen with two floors and two spans was designed, and the failure mechanism of the specimen was obtained by low-cycle loading test. The hysteretic performance, deformation capacity, energy dissipation capacity and stiffness degradation of the specimen were analyzed. The results showed that the failure mechanism of the prefabricated concrete-filled steel tubular special-shaped column is a typical beam hinge mechanism, which meets the design requirements of “strong column and weak beam”. The special-shaped columns frame of built-in concrete-filled circular steel pipe has full hysteretic curve, good ductility and energy dissipation capacity, and stable stiffness degradation. When the specimen is damaged, the inter-story drift angle reaches 1/23, which is much higher than the limit requirement of elastic–plastic inter-story drift angle of 1/50 under strong earthquake. The existence of built-in concrete-filled steel pipe changes the bearing mechanism of the structure. After the external concrete falls off, the internal force of the structure redistributes, forming a stress system of built-in concrete-filled steel pipe truss. The post-cast joint between overlapping precast column and superposed beam and grouting connection joint between precast column and column sleeve are not damaged, and the fabricated joints are safe and reliable.

Cyclic Performance of Cold‐formed Steel Moment Resisting Frames

AbstractThis paper investigates the seismic performance of a single storey moment resisting cold‐formed steel (CFS) portal frame through cyclic testing. Six monotonic and six cyclic tests were performed on three different section sizes of CFS portal frames. The portal frames were 3.2m long x 2.2m high and the CFS sections bolted with either perfect‐fit tolerance bolt holes (PTBH) or normal tolerance bolt holes (NTBH) connections. Connections with NTBH are standard in CFS, but connections with PTBH are often only used for short‐spanning frames. Results from the tests demonstrated that both PTBH and NTBH connections had stable hysteresis and good hysteretic energy dissipation capacity and ductility. On average, the NTBH connections performed better under cyclic loading in comparison to the PTBH connections (5.4% larger ductility and 22.3% increased energy dissipation). Strain gauge results show failure due to combined bending and bi‐moment stresses, of which the bi‐moment stress component accounted for 41% of the total longitudinal stresses at the section web. It should be noted that bi‐moment stresses are often incorrectly ignored by practitioners; the experimental test results thus show that by doing so the sections would fail at 59% of the design moment.