Test Results Of Connections Research Articles

FBG-based force sensing with temperature self-compensation for smart bolts

Small variations in bolt component connection can have significant impacts on equipment operating safety and efficiency. A comprehensive understanding of the bolted status supports the equipment optimizing in in-situ health monitoring. Therefore, an improved bolt force measurement method is looking forward. Given the minimally invasive nature, potential for multi-parameter measuring, and ability to operate in harsh conditions, optic fiber sensors present an opportunity for equipment in-situ health monitoring. This paper first strengthened the confidence in embedding optic fiber force sensors within the bolts. Additionally, the FBG temperature self-compensation method is employed and successfully improved the force measurement accuracy, compared with the existing studies. The smart bolt configuration (addictively manufactured) refers to the standard bolt dimensions and integrates a metallized FBG optical fiber with a diameter of less than 0.5 mm. Then, the sensor performance was investigated through a series of routine mechanics tests and reports the force sensitivity of the designed smart bolt is 13.06 pm/kN (for M10 bolts) and 14.59 pm/kN (for M12 bolts), respectively. In dynamic force loading tests, the error of the sensor is within 4.95 %, and the maximum force detection error after temperature compensation is within 8.03 %, indicating an improved bolt force measuring accuracy. The anti-creep and anti-torque interference tests were undertaken to confirm the designed smart bolts are adequate for long-term service. The bolt vibration and connection test results have proved the mechanical solidity and reliability under extreme working conditions. This investigation confirms the viability of installing optic fiber force sensors in a bolt component. Confidence was established that the smart bolts have the advantages of compact structure, improved force detection accuracy, good reliability, and support for modern equipment in-situ health monitoring.

Component-based modelling of single-leg bolted steel angle connections at elevated temperatures

As a vital part of contemporary society, steel lattice transmission towers and communication towers play an important role in the power transmission grid and telecommunication, respectively. Being often located in rural areas, they are prone to bushfire attacks due to heatwaves and droughts, which are becoming increasingly commonplace. However, unlike the steel members found in a lattice tower, the behaviour and material properties of which at elevated temperatures have been comprehensively studied and codified in design standards, the semi-rigid behaviour of the bolted connection between such members at elevated temperatures has not been investigated thoroughly. Therefore, this paper aims to investigate both the axial and rotational behaviour of single-leg bolted steel angle connections at both ambient and elevated temperatures. A theoretical model using the component method is firstly proposed to model the axial load-slip behaviour incorporating the temperature increase, with the effects of the bolt shear, plate bearing, friction between clamped members, bolt slip, and member elongation being considered. Once the axial load-slip model is proposed, the component-based model for describing the moment-rotation behaviour of the bolted connection is derived based on the load-deformation relations of individual bolts in the bolt group. The reliability of the theoretical model is then validated by modelling the connection behaviour obtained from previous connection test results. A three-dimensional finite element model is also constructed using ABAQUS software to further validate the accuracy of the proposed theoretical model for predicting the axial and rotational behaviour of single-leg bolted angle connections at elevated temperatures. It is demonstrated that the proposed component-based theoretical model for the bolted angle connection accounting for axial and rotational semi-rigidity as well as temperature elevation is capable of effectively capturing the load-deformation relationship for the single-leg bolted angle steel connections, and would be applicable to the study of steel lattice towers under bushfire attack.

Lateral Performance Simulation of Conventional CLT Shear Wall and Structure by Equivalent Decomposed Wall Model

The study aims to simulate the lateral responses of the conventional cross laminated timber (CLT) shear wall by establishing the equivalent decomposed wall models and providing lateral performance evaluation of walls with varied connections and walls in mass timber structures. First, the connection hysteresis model was built by calibrating the corresponding test results from references. Then, a detailed wall model, assembled with the calibrated connection models and shell elements, was calibrated with the wall experiments available in the literature. Based on the detailed wall model and the referred connection test results, an improved decomposed model with equivalent springs and shell elements was developed. The case studies indicate that both models captured the behavior of different connection configurations; however, the equivalent decomposed model provided a better prediction of the equivalent viscous damping ratio. The equivalent decomposed model was then applied in a full-scale three-story building time-history seismic analysis. The building simulation results indicate that the developed models can accurately estimate the wall hysteresis behavior, which can be a reference for CLT shear wall design.

Direct stiffness-strength method design for sheathed cold-formed steel structural members - Recommendations for the AISI S100

This paper presents a new design procedure for considering the bracing effect of sheathing boards that are attached to the cold-formed steel (CFS) structural members. The previous investigations show that the current AISI design specification for sheathing bracing design of CFS wall panels is unconservative (i.e. design standard predict a larger failure load than the experimental test results) due to exaggerated sheathing stiffnesses calculated from ideal loading conditions rather than worst-case loading conditions. Therefore, a new design procedure is suggested based on the performance (strength and stiffness) of the individual sheathing fastener connections. A new and simplified test setup is also introduced to simulate the realistic failure modes of the sheathing fastener connections using a conventional universal testing machine. A total of 67 individual sheathing fastener connection tests were carried out, including parameters such as ten different dimensions of the CFS stud (to account for the slenderness) and seven various sheathing board types (to account for the performance of each sheathing type). Based on the individual sheathing fastener connection test results, new expressions are formulated to predict the stiffness and strength of the individual sheathing-fastener connections. A statistical and application-oriented merit-based assessment indicated that the proposed expressions are appropriate for the use of sheathing braced design. In particular, the individual sheathing fastener-connection strength and stiffness arrived by the proposed expressions are conservative in predicting the failure mode and design strength of the sheathed CFS panel. Finally, this paper demonstrates the effectiveness of the proposed simplified design method by illustrating with the help of a design example, which quantifies the benefit of adopting this method in AISI design guidelines.

Chord-end RHS-to-RHS and CHS-to-CHS X-connections with rigid cap plates: Stress concentration factors

For rectangular hollow section (RHS)-to-RHS and circular hollow section (CHS)-to-CHS connections situated near a truss/girder end, reinforcement using a chord-end cap plate is common; however, for fatigue design, formulae in current design guidelines [for calculation of stress concentration factors (SCFs)] cater to: (i) unreinforced connections, with (ii) sufficient chord continuity beyond the connection on both sides. To develop definitive design guidelines for end connections with rigid cap plates, previous full-scale connection test results have been used to validate a finite element (FE) modelling approach, and a total of 496 FE models with different chord end distance-to-width (or diameter) (e/b0 or e/d0), branch-to-chord width (β), branch-to-chord thickness (τ), and chord slenderness (2γ) ratios have been modelled and analyzed. Existing SCF formulae in CIDECT Design Guide 8 are shown to be inaccurate if applied to cap plate-reinforced end connections. SCF correction factors (ψ), and parametric formulae to estimate ψ based on e/b0 (or e/d0), β, τ and 2γ, are derived.

Cyclic Experiments on Sidelap and Structural Connectors in Steel Deck Diaphragms

This work studied the cyclic shear performance of connectors used for sidelap and structural connectors in bare steel deck roof diaphragms. Typical bare steel deck roof diaphragms include thousands of such connections, and knowledge of the connection shear performance is important for understanding and predicting diaphragm performance under seismic loads. The experimental program included four types of sidelap connectors: screw nestable, top arc seam weld, button punch, and the proprietary PunchLok II crimp. The testing included three types of structural connectors: power-actuated fasteners, arc spot welds, and arc seam welds. A total of 64 sidelap and 60 structural connector tests were performed under a cyclic loading protocol, to evaluate behavior at small deformations as well as under large excursions, providing the shear response up to and through the peak response, including postpeak response until material separation and failure. The connection test results were used to establish experimental multilinear backbone curves. From these backbone curves, average connection shear stiffness, strength, and ductility can be estimated and compared for all studied configurations. The connection response for the mechanical connections and welded connections exhibited significantly different behavior, particularly in terms of postpeak ductility and residual force. The connector backbone response is appropriate for use as nonlinear shear springs to model the response of the connections in high-fidelity models of bare steel deck roof diaphragms.

Experimental Study of Cold-Formed Steel Moment Connections with Screw Fasteners

A series of connection with screw fasteners were tested to study the behavior of cold-formed steel moment connection. The test specimens included hot-rolled parallel flange channels, cold-formed lipped C-Channels, and self-drilling self-fastening screws. Two different lipped C-Channels and a various number of screws per connection were used in this study. The moment-rotation behavior, rotational rigidity, and the connection capacity differed with the number of screws. The connection behaved as a pinned connection when 4 screws were used. However, local buckling was observed in the cold-formed steel sections near the connection when 8, 10 and 14 screws were used. The connection test results were compared with theoretical results calculated in accordance to the Australian Standards. None of the connection tested could achieve the moment capacity of the section connected.

Clinical-neuropsychological features of the hepatic encephalopathy formation

35 patients with different stages of the hepatic encephalopathy on the background of the chronic hepatitis at the age of 45.2 ± 5.8 years were examined. The investigation complex included neurological, psychometric (numbers connection test, SDMT number-symbol test, Schulte tables, Montreal cognitive function evaluation scale, HADS scale), and instrumental (EEG and MRI of the brain) examination. The findings showed that early clinical manifestation of hepatic encephalopathy included mild cognitive impairments, sleep disturbances (initial manifestations of impaired consciousness), emotional disorders (asthenic syndrome, anxiety) and impaired fine motor movements (changes of handwriting and fine coordination). According of the psychometric testing results the signs of the hepatic encephalopathy latent stage were detected including an impairment of the attention (due to numbers connection test results), a decrease of the cognitive processes speed and a violation of visual short-term memory (SDMT), difficulty in delayed reproduction of the information, a violation of fine motor movements (change handwriting). Disturbance of the brain bioelectrical activity was characterized by slowing the frequency of the alpha rhythm, an increase in the slow-wave activity index, smoothed zonal differences, and recording of hypersynchronous alpha waves or three-phase waves, which were determined already in the early stages of the disease. Comparing the psychometric testing data and the neuroimaging results, it was noted that the identified cognitive disorders, including those at the latent stage of hepatic encephalopathy, were accompanied by the frontal and parietal lobes cortex hypotrophy and the subcortical structures damage. Progression of the hepatic encephalopathy was accompanied by increased cognitive, emotional, motor and sleep disorders, which was confirmed by the results of psychometric testing, and also coincided with the functional and morphological disorders worsening of the brain according to the neurophysiological and neuroimaging examinations.

Effects of L-ornithine-L-aspartate on the manifestation of minimal hepatic encephalopathy in the dynamics of cytostatic therapy

Objective — to investigate effects of the L-ornithine-L-aspartate (LOLA, Hepa-Merz®) on the clinical manifestations of minimal hepatic encephalopathy (HE) in patients with multiple myeloma (MM) in the dynamics of cytostatic treatment (CT).Materials and methods. The study involved 42 patients with MM who never received CT, from them 18 (42.8 %) men and 24 (57.2 %) women, aged 62.3 ± 8.67 years. Depending on the LOLA (Hepa-Merz®) administration, patients were divided into two groups: group I (n = 20) included patients with MM treated with CT; group II (n = 22) consisted of patients with MM, who additionally were treated with LOLA (Hepa-Merz®) at a daily dose 15 g orally throughout the observation period. The assessment of the patients’ condition was carried out twice: before the treatment and on the 56th day. The parameters of complete blood count, biochemical panel were analyzed; the number connection test was performed.Results. At baseline, in 28 (66.7 %) patients with MM minimal HE was present, which was accompanied by changes in the biochemical panel that correspond to the MM active phase. After two CT courses with no additional LOLA (Hepa-Merz®), the serum creatinine level decreased in 1.8 times (p < 0.05), the HE manifestations reduced according to number connection test results. However, the gamma-glutamyltransferase activity increased in 2.3 times more than normal (p < 0.05). In patients of group II who received the combination of CT and LOLA (Hepa-Merz®), the serum creatinine decreased in 1.8 times compared to the baseline level (p < 0.05), accompanied by HE frequency and degree reduction without functional liver tests violations.Conclusions. Administration of LOLA (Hepa-Merz®) is recommended for patients with MM during CT, it effectively eliminates the manifestations of minimal HE and shows a protective effect on the hepatocytes.

Compressive and racking performance of eccentrically aligned dou-gong connections

This paper presents an experimental study on the compressive and racking performance of eccentrically aligned dou-gong connections used in Chinese traditional timber structures. Four 1:3.4 scaled specimens were fabricated and tested with static compressive and cyclic lateral loading. The damage modes and load–displacement (or hysteresis) curves of the dou-gong connections as well as the influence of the composite action effect and vertical compression loading were discussed. It was found that the load–displacement curve of an eccentrically aligned dou-gong connection was nearly bilinear and the change of the vertical stiffness took place when the cap block cracked and loosened the lateral constraint on the overturning of the connection. The vertical initial compressive stiffness was nearly 70% of a concentrically aligned dou-gong connection according to a predictive formula established based on concentrically aligned dou-gong connection test results. The initial stiffness, yield load and maximum load of double dou-gong connections were found to be 262%, 332% and 373% of those of a single dou-gong connection, respectively. The composite action from the interlocked straight beams (by shear keys) and infill panel can increase the lateral stiffness by more than 55% and the energy dissipation capacity by more than 70%, though such composite action decreases with the worn out of the contact surfaces of the straight beams and the plastic deformation of the shear keys. The vertical load improved the stiffness and energy dissipation capacity of the connections mostly by the friction force. Specifically, an increase of 120% in the vertical compression load can lead to more than 50% increase in the lateral stiffness and up to 130% increase in the energy dissipation capacity.

Performance of semirigid timber frame with Lagscrewbolt connections: experimental, analytical, and numerical model results

This paper presents analytical and numerical models for semirigid timber frame with Lagscrewbolt (LSB) connections. A series of static and reverse cyclic experimental tests were carried out for different beam sizes (400, 500, and 600 mm depth) and column–base connections with different numbers of LSBs (4, 5, 8). For the beam–column connections, with increase in beam depth, moment resistance and stiffness values increased, and ductility factor reduced. For the column–base connection, with increase in the number of LSBs, the strength, stiffness, and ductility values increased. A material model available in OpenSees, Pinching4 hysteretic model, was calibrated for all connection test results. Finally, analytical model of the portal frame was developed and compared with the experimental test results. Overall, there was good agreement with the experimental test results, and the Pinching4 hysteretic model can readily be used for full-scale structural model.

Experimental Studies on Seismic Performance of Precast Steel Reinforced Concrete Frame and Connections

A new type of precast steel reinforced concrete (PSRC) frame, which were composed of composite steel reinforced concrete (CSRC) beam, PSRC column and cast-in-situ (CIS) joint, were proposed in this paper. The assemble technique used in the ordinary steel structures were adopted in PSRC frames to improve the construction efficiency. The seismic performance of PSRC frame structures was investigated based on the test results of connections and frame. Firstly, full-scale internal connection specimens, including a CIS connection specimen RCJ-1 and a PSRC connection specimen PCJ-1, were tested under low reversed cyclic loading. Results revealed that both the specimens RCJ-1 and PCJ-1 exhibited similar performance in terms of loading capacity, stiffness degradation and energy dissipation. The ductility of specimen PCJ-1 was about 3.81, which was a little lower than the specimen RCJ-1. Then, a 1/3-scale PSRC frame structure specimen, namely PCF-1, was tested under low reversed cyclic loading. Results showed that the PSRC frame specimen PCF-1 was failed in mixed failure mechanism, which provide good energy dissipation capacity. The ductility coefficient of PCF-1 was about 3.45 indicating that the PCF-1 behaved in ductility manner. The results of this investigation could enrich the data available documenting the behavior of PSRC frame, and contribute to enlarge the application of PSRC frame structures in seismic zone.

Strength of Loop Connections between Precast Bridge Decks Loaded in Combined Tension and Bending

The paper presents a study of the load-carrying capacity of loop connections subjected to combined tension and bending. For such connections, the main design challenge in practice is to obtain a load- carrying capacity that is governed by yielding of the looped reinforcing bars (i.e., the U-bars) and not by fracture of the joint concrete. Unfortunately, reliable design models serving this purpose have not yet been published. Therefore, in this paper, a design-oriented plasticity model is proposed for the calculation of the N–M interaction diagram accounting for both failure modes. The work is an extension of a model previously developed by the authors for the case of pure tension. In addition to the theoretical work, test results of connections subjected to combined tension and bending are also presented. Calculations according to the model have been compared with tests. Satisfactory agreements have been found.

Psychomotor recovery and blood propofol level in colonoscopy when using propofol sedation

It is commonly recommended that patients refrain from driving for 24 hours after endoscopy for which sedation is given. The aim of this study was to evaluate psychomotor recovery and blood propofol concentrations after colonoscopy with propofol sedation to determine whether driving might be safe. A prospective, consecutive study. Municipal hospital outpatients. This study involved 48 consecutive patients scheduled for colonoscopy with propofol sedation. Patient clinical features, psychomotor recovery, and blood concentrations of propofol were assessed. Psychomotor recovery was assessed before colonoscopy and 1 and 2 hours after colonoscopy by using the number connection test and a driving simulator test. Clinical features, psychomotor recovery, and blood concentration of propofol. All patients successfully completed the post-sedation assessments. Although there was a significant difference in results of the number connection test between before colonoscopy and 1 hour after colonoscopy, all number connection test results were within normal limits (<40 seconds). Scores were as follows: mean time (standard deviation) before colonoscopy, 32.2 (2.0) seconds (range 29-36 seconds) versus after colonoscopy, 32.7 (2.0) seconds (range 27-38 seconds); P = .0019. Driving skills had recovered to the baseline levels 1 hour after colonoscopy. Scores were as follows: tracking error (%) before colonoscopy, 45.0 (5.6) versus after colonoscopy, 46.0 (5.5); P = .61; accelerating reaction time in seconds before colonoscopy, 0.65 (0.15) versus after colonoscopy, 0.62 (0.14); P = .40; braking reaction time in seconds before colonoscopy, 0.58 (0.13) versus after colonoscopy, 0.61 (0.13); P = .50. Small sample size, single-center study. Although consistent findings on the number connection test and driving simulation (psychomotor recovery) test are present as early as 1 hour after propofol sedation, a study of additional numbers of patients as well as different patient populations are needed before these results can be universally recommended.

A Geosynthetic Modular Block Connection Creep Test Apparatus, Methodology, and Interpretation

Abstract A test protocol for the quantification of creep between modular block (segmental) facing units and geosynthetic reinforcement can be found in a Federal Highway Administration guidance document first published in 2001. However, to date the utility of the proposed method has not been examined in a systematic manner nor have test results been reported in the research literature. The paper describes a test apparatus and reports the results of a series of connection creep tests that demonstrate details of the proposed methodology and lessons learned. Important recommendations for data interpretation are presented for the first time. An additional practical result of this study is a consistent method to calculate the connection creep reduction factor required for design using the results of conventional short-term connection test results and connection creep-rupture curves.

Development of Cold-Formed Steel Portal Frames with PRY Sections

A series of column, beam, and connection tests for portal frames which consisted of closed cold-formed steel PRY sections as columns and rafters were carried out. Firstly the compressive and the flexural strengths of the PRY sections were investigated, and secondly the structural behavior of the connections including the moment-rotation relation, the yield and the ultimate moment capacities of the connections were studied. The connection test specimens consisted of column-base, column-to-rafter, and rafter-to-rafter connections. The main testing parameters of the connection tests were the thickness and the shape of mild steel connectors, which were important for the proposed attachment system of wall panels. The connection test results were compared with those achieved by using advanced analysis procedures. The semi-rigid connection concept was considered appropriate for the analyses of the portal frames using the secant stiffness of the connections, which were estimated from the measured moment-rotation curves of the connections tested. Simple formulae for the shear resistances of the screwed connections were also proposed after calibrated with test results. The performance of the portal frame with PRY sections was investigated through the full scale tests.

Cyclic behaviour of post-Northridge WUF-B connections

The purpose of this study is to evaluate the cyclic behavior of post-Northridge Welded Unreinforced Flange-Bolted web (WUF-B) connections made using new notch tough welding materials and welding procedures, and a modified access hole. Since no WUF-B connection test results were found which satisfy the minimum design and detail requirements of the 2002 AISC Seismic Provisions for Structural Steel Buildings, this study made three full-scale test specimens of WUF-B connections according to the provisions. The main variable of the specimens was the ratio of the panel zone strength to the connected beam strength (panel zone strength ratio). Quasi-static cyclic testing was conducted. This study found that post-Northridge WUF-B connection specimens having a stronger panel zone experienced more significant slip between the bolted shear tab and the beam web. It was observed that the slip caused stress concentrations in and around the access hole, resulting in connection failure. The WUF-B connection specimen having the weakest panel zone did not, however, experience excessive slip between the bolted shear tab and beam web. Moreover, this WUF-B specimen could not achieve the required beam strength. This study observed that post-Northridge WUF-B connections with a panel zone strength ratio ranging from 0.9 to 1.6 provides a drift ratio exceeding 0.2. This drift ratio is required for satisfactory performance of the connections of Intermediate Moment Frames. Furthermore, this study proposed an analytical model for post Northridge WUF-B connections having different panel zone strength ratios.

Modelling M–φ curves for standard beam-to-column connections

A 3-parameter exponential model to describe the non-linear M–φ relationship of flexible beam-to-column connections is proposed. The model only requires a determination of the parameters M o, K i, and K p generated from a connection's dimensional details and material strength properties. Employing simplified connection behavioural models to approximate beam-to-column connection behaviour and from kinematic and equilibrium considerations, analytical expressions for evaluating the model parameters K i and K p are derived for standard beam-to-column connections; an empirical expression for evaluating the M o-parameter is developed. The connection M–φ behaviour predicted by the model is compared with published connection test results and it is concluded that the model yields results in good agreement with actual connection test behaviour.

Fracture Strength of Welded Flange-Bolted Web Connections

In 1994, California's steel building frames withstood the 6.8 magnitude Northridge earthquake without collapse or casualties. Severe damage, however, was sustained by the welded flange-bolted web connections: at the column-weld interface brittle fractures were discovered. Using linear elastic fracture mechanics this unexpected failure mechanism is explored in this work. Post-Northridge connection test results and recent finite-element studies supply the springboard for this investigation of the fracture strength of welded flange-bolted web connections. A method of predicting the brittle fracture strength of these connections is presented and validated. The probability of brittle fracture is also investigated.

The number connection tests A and B: interindividual variability and use for the assessment of early hepatic encephalopathy

Background/Aims: The number connection tests A and B are regarded as sensitive psychometric measures for the assessment of early hepatic encephalopathy. Review of the studies dealing with the diagnostic sensitivity of the number connection tests, however, shows that the scoring of the number connection tests results differs between studies. Most groups define the limits of the normal range by studying small control groups. Others use scores given in the literature without ensuring the comparability of the test versions used. Thus, there is a need for normative data for the number connection test results and for re-evaluation of the sensitivity of the tests using valid scores. Methods: In this study the number connection tests A and B were administered to 249 healthy volunteers (age: 18 to 76 years) to analyze the influence of age, education and occupation on their results. In addition, the age-corrected normative data were applied to 169 patients with grade 0-I hepatic encephalopathy. The specificity and sensitivity of age-corrected and age-independent normative data of the number connection tests were compared. Results: There was a significant influence of age and education on the number connection test results, but only a negligible effect of occupation. Application of the age-corrected normative data to the test results of the patients with grade I hepatic encephalopathy significantly decreased the sensitivity of the number connection tests for hepatic encephalopathy compared to widely used age-independent normal ranges, but also increased the specificity. Conclusion: The use of standardized versions of the number connection tests and age-related normative data is recommended.