Rotation Demands Research Articles

11.53: Reduced cross‐sections in seismic resistant steel structures

ABSTRACTIn case of flexural dissipative members in eccentrically braced frames, a detail with reduced beam flanges sections at the link ends leads to a better control of the inelastic deformations along the dissipative member, together with a reduction of the plastic hinge rotation demand and with significant lateral stiffness of the braced frame.Configurations resembling the “dog‐bone” near the ends of the upper stories diagonals in concentrically braced frames ensure on one hand, the abidance of the slenderness demand for the braces and on the other hand, small values of the amplification ratio Ωi(N)=NplRd,i/NEd,i. The reduced cross‐section of the diagonal in the “dog‐bone” detail zones ensures an adequate tensile capacity of the braces and small Ωi(N) values. At the same time the buckling behaviour and slenderness of the braces is not significantly affected by the reduced cross‐sections near the member ends and the slenderness demand of the braces will be fulfilled.A favourable global plastic hinge mechanism can be sized by design for concentrically braced frames by providing configurations with reduced cross‐sections for potentially plastic zones located in the frame girders in the neighbourhood of the beam/column connections. So plastic deformations can develop in the braces, at the bottom of first‐story columns and in potentially plastic zones located near the ends of frame girders, and a favourable global plastic failure mechanism can be achieved. The same design concept can be used for sizing a favourable global plastic mechanism for frames with rigid beam/columns connections equipped with buckling restrained braces.Configurations with “dog‐bone” details near the base of bottom‐story columns appear to be safer from the point of view of assuring the general stability of the first‐story column in the situation when plastic deformations occur in the potentially plastic zone at the bottom of the column. Further, a better control of the plastic deformations along the first story columns is ensured.

INVESTIGATION OF WEIGHT-BEARING SYMMETRY IN A GROUP OF ATHLETES WITH LOW BACK PAIN AND HEALTHY PEOPLE DURING GAIT

The asymmetrical loading applied to legs was proposed as a risk factor for low back pain development. However, this proposed mechanical risk factor was not investigated in the athletes with LBP engaged in rotational demand activities. The aim of the present study was to examine symmetry of weight-bearing in patients with rotational demand activities compared to that in healthy people during gait. In total, 35 subjects, 15 males with LBP and 20 males without LBP, participated in the study. The participants were asked to walk 12 trials in gait lab. Forces applied to legs were recorded by a force plate. Then, the peaks of anteroposterior, mediolateral, and vertical forces were measured. Next, the asymmetrical loads applied to the legs were calculated. The results of our study demonstrated that people with LBP exhibit more asymmetry of vertical peak forces in heel strike and mid-stance. They also exhibited more asymmetry of loading in the anterior direction. But the mean values of ASI of mediolateral and posterior forces in these participants were not significantly different compared to those in the control group. It can be concluded that, in comparison to the healthy subjects, patients with LBP walk with a greater magnitude of asymmetrical weight-bearing at a comfortable speed.

Patient reported activities after reverse total shoulder arthroplasty in rotator cuff arthropathy patients

Introduction and objectiveReverse total shoulder arthroplasty in rotator cuff arthropathy patients, improves anteversion and abduction, but not rotational, outcomes. The main aim of this study is to determine its repercussions on daily life activities in our patients. Material and methodsBetween 2009 and 2011 we implanted 210 shoulder arthroplasties, 126 of them were reverse total shoulder arthroplasty in a rotator cuff arthropathy context. About 88% were women, with a mean age at time of surgery of 81 years, 95% were retired. The mean follow up was 53 months. The Constant scale, Visual Analogue Scale, Charlson Comorbidity Index, and range of motion were measured for each patient and whether they could manage 40 daily life activities by means of a new questionnaire, classifying them according to shoulder functional demand. Results and discussionMean normalised by sex and age Constant value was 81.2%. Mean Visual Analogue Scale and Charlson Index were 3.56 and 1.69 respectively. Improvement in anteversion and abduction, not in rotational range of motion. Limitation was found in low and high functional demand activities in 20% and 51% respectively, especially those which involved internal rotation. ConclusionReverse total shoulder arthroplasty treatment for RCA in the elderly, achieves adequate pain management and good functional outcomes. Nevertheless, an important risk of DLA limitation must be accepted in those which involve internal rotation or shoulder high functional demand.

Actividades de vida afectadas en pacientes tras artroplastia total inversa de hombro en el contexto de artropatía de manguito rotador

Introduction and objectiveReverse total shoulder arthroplasty in rotator cuff arthropathy patients, improves anteversion and abduction, but not rotational, outcomes. The main aim of this study is to determine its repercussions on daily life activities in our patients. Material and methodsBetween 2009 and 2011 we implanted 210 shoulder arthroplasties, 126 of them were reverse total shoulder arthroplasty in a rotator cuff arthropathy context. About 88% were women, with a mean age at time of surgery of 81 years, 95% were retired. The mean follow up was 53 months. The Constant scale, Visual Analogue Scale, Charlson Comorbidity Index, range of motion were measured for each patient and whether they could manage 40 daily life activities by means of a new questionnaire, classifying them according toshoulder functional demand. Results and discussionMean normalized by sex and age Constant value was 81.2%. Mean Visual Analogue Scale and Charlson Index were 3.56 and 1.69 respectively. Improvement in anteversion and abduction, not in rotational range of motion. Limitation was found in low and high functional demand activities in 20% and 51% respectively, especially those which involved internal rotation. ConclusionReverse total shoulder arthroplasty treatment for RCA in the elderly, achieves adequate pain management and good functional outcomes. Nevertheless, an important risk of DLA limitation must be accepted in those which involve internal rotation or shoulder high functional demand.

Experimental and analytical analysis of moment-resisting connections with glued-in rods

Abstract The advances of timber engineering in the field of tall buildings raised a need for high performance connections that can accommodate increased demands due to higher loads and longer spans. A semi-rigid connection with glued-in rods was designed to fulfill these requirements. Moment-rotation behavior of this connection was investigated in a series of quasi-static cyclic tests. A moment-resisting connection was established between timber columns and steel base plates. Three different timber products, including hardwood and softwood species, and two different rod diameters were used. The columns were subjected to shear force and bending, to simulate the loading conditions of a column in a frame under lateral loads. The tests were performed with increasing rotation demand on the column until the failure. The connections provided high moment capacity and rotational stiffness. All of the tested specimens demonstrated ductile response, while the connections with hardwood performed especially well. No strength degradation was observed in multiple cycles, therefore the hysteretic energy dissipation was significant in cycles with high target displacement. The nature of the connection response was studied in detail and an analytical model was developed to describe the relationship between the moment and the rotation at the column base. The model is capable to predict the envelope of the cyclic response and corresponds well to the experimental results.

Seismic applicability of a long-span railway concrete upper-deck arch bridge with CFST rigid skeleton rib

To determine the seismic applicability of a long-span railway concrete upper-deck arch bridge with concrete-filled steel-tube (CFST) rigid skeleton ribs, some fundamental principles and seismic approaches for long-span bridges are investigated to update the design methods in the current Code for Seismic Design of Railway Engineering of China. Ductile and mixed isolation design are investigated respectively to compare the structural seismic performances. The flexural moment and plastic rotation demands and capacities are quantified to assess the seismic status of the ductile components. A kind of triple friction pendulum (TFP) system and lead-plug rubber bearing are applied simultaneously to regularize the structural seismic demands. The numerical analysis shows that the current ductile layout with continuous rigid frame approaching spans should be strengthened to satisfy the demands of rare earthquakes. However, the mixed isolation design embodies excellent seismic performances for the continuous girder approaching span of this railway arch bridge.

KINEMATIC DIFFERENCES IN LUMBOPELVIC AND HIP MOVEMENT PATTERNS DURING A LOWER LIMB MOVEMENT TEST BETWEEN TWO GROUPS OF PEOPLE WITH LOW BACK PAIN

Increased lumbopelvic motion during limb movements’ tests was reported in low back pain (LBP) patients with and without rotational demand activities. The aim of this study was to compare lumbopelvic movement pattern between two groups of LBP patients with and without rotational demand activity during active hip external rotation test. A total of 39 patients with non-specific chronic LBP participated in this study. Patients were allocated into two groups, in first group 15 subjects (mean [Formula: see text] years) with rotational demand activities such as tennis, squash and golf, and in second group 24 subjects (mean [Formula: see text]) without rotational demand activities participated in current study. Kinematic data from lumbopelvic-hip region during active hip external rotation test (AHER) were collected by a 3D motion analysis system. Variables including range of motion (ROM) of hip external rotation, pelvic rotation, pelvic rotation during first half of hip rotation motion and timing of pelvic-hip movement were calculated by MATLAB software for both sides and after this, independent t-test was used to compare the variables between two groups of study. The mean lumbopelvic rotation in lower extremities tests for both sides and lumbopelvic rotation in the dominant limb external rotation test in the patients with rotational demand activities were significantly more than other group ([Formula: see text]). During dominant lower limb movement test, pelvic rotation in first half of movement and in patients with rotational activities was greater than in non-rotational group but hip rotation was statistically lesser than other group ([Formula: see text]). Other variables between the two groups were not significantly different ([Formula: see text]). The result of the study suggest that LBP patients who have rotational demand sports activities may move their lumbopelvic region in a greater magnitude during the AHER test than LBP people without rotational demand activities. Therefore, Lumbopelvic movement pattern in different groups of patients with LBP and based on their specific activities is different with each other.

Progressive Seismic Failure of a Highway Bridge, Including Abutment-Backfill Interaction

Current engineering practice pays little attention, if any, to nonlinear abutment-backfill soil interaction (ABSI) effects on seismic behaviour of bridges. The primary focus of this article is to assess the influence of ABSI on the progressive seismic failure of bridge structures. Emphasis is placed on the significance of ABSI effects, including abutment behaviour and backfill soil flexibility. Nonlinear dynamic analysis is performed using a bilinear hysteretic model for the bridge superstructure and nonlinear characteristics of the expansion joint. Results indicate that ABSI has a significant effect on the seismic response in the longitudinal direction and can effectively reduce bridge seismic demands. ABSI affects rotational ductility demand at pier ends of the bridges, relative displacements, pounding and axial forces in the restrainers. Thus, it is essential that numerical models used in seismic assessment of bridge structures properly consider abutment-backfill interaction.

Fluid viscous dampers locations in reinforced-concrete core wall buildings

Conventionally, a flexural plastic hinge is assigned and detailed at the core wall base and coupling beams ends to control seismic responses. This strategy is based on allowing damage to main structural components. To avoid damage to main structural components, an alternative strategy using energy dissipating devices, such as fluid viscous dampers (FVDs), is currently being studied and implemented. In this study, the effect of FVD locations on a 40-storey, high-rise, reinforced-concrete core wall case study building has been studied in detail using non-linear response history analysis for seven spectrally matched ground motions. FVDs were installed at strategic locations, identified based on maximum ‘design basis earthquake’ elastic modal racking shear deformation demands and force (shear and moment) demands in three different options. The force, deformation and energy demands on structural components are compared for conventional design and different options of FVDs. The comparison with conventional design shows that FVDs are effective not only for reducing shear force demand along wall height, bending moment demand at mid-height and deformation demands by 10, 45 and 35%, respectively, but also significantly reduce the rotation and energy demands in the core wall by 60 and 450%, respectively.

Failure analysis of a welded steel pipe at Kullar fault crossing

Abstract The seismic response of a 2200-mm-diameter welded steel pipe at strike slip Kullar fault crossing in Izmit, Kocaeli during 1999 Kocaeli earthquake is investigated. The pipe was crossing the fault-line with an angle of 55° and suffered leaks due to 3.0 m of right lateral movement of fault, which imposed compressive axial strain in the pipe. The backfill material of the trench was native soil which was non-homogenous (soft and stiff clay) with respect to fault line-soft material on the North side, stiff material on the South side. Field observations revealed two major wrinkles with finger width cracks and a minor wrinkle on the soft soil side of the fault. Large plastic strains and local folding were observed at wrinkles due to compressive strains. The case is known as one of the best documented fault crossing examples. The failure behavior of the Thames water pipe during 1999 Kocaeli earthquake is simulated by utilizing a 3D nonlinear continuum FE model. The numerical model considers contact surface at soil pipe interface and performs large deformation analyses of the pipe. The locations of wrinkles as well as axial displacements/rotations demands due to fault rupture are predicted. It is observed that once wrinkle initiates, strain in the pipe away from the wrinkle reduces after initial local buckling and additional shortening of the pipeline tends to accumulate at the wrinkle causing large plastic strains and rotation demands associated with fault rupture, an observation consistent with field observations and 2005 ALA guidelines.

Strength and stiffness modeling of extended endplate connections with circular and rectangular bolt configurations

The results of a series of finite element (FE) simulations and experimental studies are used to develop strength and stiffness models that predict the failure capacity and response characteristics of unstiffened extended endplate connections with circular and rectangular bolt configurations associated with deep girders. The proposed stiffness models are composed of multi-linear springs which model the overall extended endplate/column flange system deformation and strength of key-components. Comparison of model predictions with FE and experimental results available in the literature show that the proposed models accurately predict the strength and the response of extended endplate/column system with circular and rectangular bolt configurations. The effect of the bolt configuration (circular and rectangular) on the prying phenomenon encountered in the unstiffened extended endplate/column system was investigated. Based on FE results, extended endplate with circular bolt configuration has a more ductile behavior and exhibits higher total prying forces. The proposed models can be used to design connections that cover all possible failure modes for extended endplate with circular bolt configuration. This study provides guidelines for engineers to account for the additional forces induced in the tension bolts and for the maximum rotational capacity demand in the connection which are required for seismic analysis and design.

Modification of Impulse Generation During Pirouette Turns With Increased Rotational Demands.

This study determined how dancers regulated angular and linear impulse during the initiation of pirouettes of increased rotation. Skilled dancers (n = 11) performed single and double pirouette turns with each foot supported by a force plate. Linear and angular impulses generated by each leg were quantified and compared between turn types using probability-based statistical methods. As rotational demands increased, dancers increased the net angular impulse generated. The contribution of each leg to net angular impulse in both single and double pirouettes was influenced by stance configuration strategies. Dancers who generated more angular impulse with the push leg than with the turn leg initiated the turn with the center of mass positioned closer to the turn leg than did other dancers. As rotational demands increased, dancers tended to increase the horizontal reaction force magnitude at one or both feet; however, they used subject-specific mechanisms. By coordinating the generation of reaction forces between legs, changes in net horizontal impulse remained minimal, despite impulse regulation at each leg used to achieve more rotations. Knowledge gained regarding how an individual coordinates the generation of linear and angular impulse between both legs as rotational demand increased can help design tools to improve that individual's performance.

Design of Thick Plate Double-Tee Connections for Seismic Applications

AbstractDesign of thick plate double-Tee connections is discussed and evaluated based on experimental data and analytical studies. This paper summarizes the results of an extensive experimental and analytical work aiming at widening the applicability of double-Tee connections needed for deep beams that meet the performance requirements for moment-resisting frames (MRFs) in seismic areas as specified in seismic provisions. New limit states controlling the strength and deformation capacities of the connections are presented. A detailed comprehensive design methodology and design examples of thick plate double-Tee connections are developed. The proposed design procedure includes all possible yielding mechanisms and failure modes that might occur in thick plate double-Tee connections and accounts for the maximum rotational capacity demand in the connection, as required for seismic analysis and design. The information presented in this paper can be used toward prequalification of thick plate double-Tee connect...

Cyclic tests of all-steel web-restrained buckling-restrained brace subassemblages

In this study, cyclic tests of a buckling-restrained brace (BRB) subassemblage with an all-steel web-restrained brace (WRB) were conducted to investigate hysteretic behavior under combined axial and rotational demands. Four full-scale WRB frame subassemblages were subjected to the quasi-static displacement protocol used for BRB qualification described in the AISC 341–10 Seismic Provisions for Steel Buildings. Three different sizes of steel core plates were examined. One specimen used a nominal 7.9-mm thick by 152-mm wide plate, two WRB specimens used a nominal 12.7-mm thick by 152-mm wide plate, and one specimen used a nominal 12.7-mm thick by 229-mm wide plate. All specimens successfully completed the cyclic testing up to 2% story drift without experiencing brace instability, brace end connection failure, or rupture. Specimens with a 12.7-mm thick core plate survived additional cycles at 1.5% story drift before rupture. The test results also showed that the maximum compression forces were less than 1.3 times the maximum tension forces for each cycle corresponding to a deformation greater than the yield displacement, demonstrating that compression overstrength of the WRB was comparable with typical BRBs.

Whole-Body Balance Regulation during the Turn Phase of Piqué and Pirouette Turns with Varied Rotational Demands.

To compare dancers' balance regulation at the whole-body level under increased rotational demands during the turn phase of turns with and without large center-of-mass (CM) translation (i.e., piqué vs pirouette turns). Ten dancers performed single and double piqué and pirouette turns while kinematics and reaction forces were measured. During the turn phase, initial CM velocity, vertical alignment of the CM, mean braking force, and moment about the CM were compared across turn conditions using within-subject (Cliff's analog of Wilcoxon-Mann-Whitney test, adjusted for multiple comparisons) and group (sign test) statistical methods. For both single and double turns, the piqué turn phase was initiated with a significantly larger CM velocity towards the base of support than during the pirouette, consistent with the mechanical objectives of the turn. Additionally, during the turn phases of both single and double turns, the CM during the pirouette turns was more vertically aligned with the base of support than it was during the piqué turns. As rotational demand increased in both turns, the reaction forces were regulated in two ways to minimize the CM horizontal velocity as it approached vertical alignment with the base of support. By controlling the braking force and moment applied about the CM early during the turn phase, the potential for the CM to remain vertically aligned with the base of support increased. These findings can assist development of training tools geared towards balance regulation during pirouette and piqué turns.

Chord rotation demand for effective catenary action of RC beams under gravitational loadings

Many experimental and analytical studies have been conducted with beam-column subassemblages composed of a two-span beam to investigate the progressive collapse resistance of RC frames. Most study results reveal a strength-decreased transition phase in the nonlinear static load-deflection curve, which may induce dynamic snap-through response and increase the chord rotation demand for effective catenary action (ECA). In this study, the nonlinear static response is idealized as a piecewise linear curve and analytical pseudo-static response is derived for each linearized region to investigate the rotation demands for the ECA of the two-span RC beams. With analytical parameters determined from several published test results, numerical analysis results indicate that the rotation demand of 0.20 rad recommended in the design guidelines does not always guarantee the ECA. A higher rotation demand may be induced for the two-span beams designed with smaller span-to-depth ratios and it is better to use their peak arch resistance (PAR) as the collapse strength. A tensile reinforcement ratio not greater than 1.0% and a span-to-depth ratio not less than 7.0 are suggested for the two-span RC beams bridging the removed column if the ECA is expected for the collapse resistance. Also, complementary pseudo-static analysis is advised to verify the ECA under realistic dynamic column loss even though the static PAR is recovered in the nonlinear static response. A practical empirical formula is provided to estimate an approximate rotation demand for the ECA.

Modification of impulse generation during piqué turns with increased rotational demands

During initiation of a piqué turn, a dancer generates impulse to achieve the desired lateral translation and whole-body rotation. The goal of this study was to determine how individuals regulate impulse generation when initiating piqué turns with increased rotational demands. Skilled dancers (n=10) performed single (∼360°) and double (∼720°) piqué turns from a stationary position. Linear and angular impulse generated by the push and turn legs were quantified using ground reaction forces and compared across turn conditions as a group and within a dancer using probability-based statistical methods. The results indicate that as the rotation demands of the piqué turn increased, the net angular impulse generated increased whereas net lateral impulse decreased. Early during turn initiation, the free moment contributed to angular impulse generation. Later during turn initiation, horizontal reaction forces were controlled to generate angular impulse. As rotational demands increased, the moment applied increased primarily from redirection of the horizontal reaction force (RFh) at the push leg and a combination of RFh magnitude and moment arm increases at the turn leg. RFh at each leg were coordinated to limit unwanted net linear impulse. Knowledge of observed subject-specific mechanisms is important to inform the design of turning performance training tools.

Displacement-based design of steel moment resisting frames with partially-restrained beam-to-column joints

This article presents a method for the direct displacement-based design of steel moment resisting frames, with specific consideration of beam-to-column joint characteristics. The method can be used for steel frames having any type of beam-to-column joints, from rigid and full-strength to semi-rigid and partial-strength. The plastic rotation capacity of the joints is explicitly taken into account within the performance criteria for the design. To assess the accuracy of the method in controlling performance, case study structures were first designed and subsequently analysed using non-linear dynamic analysis with a set of real accelerograms. For all cases, the mean of peak inter-storey drift demands and the mean of peak plastic rotation demands on joints were controlled in accordance with the limits set during design. The results obtained demonstrate that the proposed method is appropriate for the performance-based seismic design of steel moment resisting frames with different joint typologies.

Effect of Buckling Restrained Braces Locations on Seismic Responses of High-Rise RC Core Wall Buildings

Conventionally, a flexural plastic hinge is designed and detailed at the core wall base and coupling beams ends to control the seismic responses. This strategy is based on allowing the damage to be concentrated on main structural components. To avoid such damage, an alternative strategy using energy dissipating devices (EDDs) such as buckling restrained braces (BRBs) is being studied and implemented nowadays. In this study, effect of BRBs locations on forty- (40-) story high-rise RC core wall case study building has been studied in detail using Nonlinear Response History Analysis (NLRHA) for seven spectrally matched ground motions. BRBs have been installed at critical locations identified with respect to the maximum DBE elastic modal racking shear deformation demands and force (shear and moment) demands in three different options. The force, deformation, and energy demands on structural components are compared for conventional design and different options of BRBs. The comparison with conventional design shows that BRBs not only are effective for reducing shear force demand along wall height, bending moment demand at mid height, and deformation demands by 10%, 45%, and 45%, respectively, but significantly reduce the rotation and energy demands in the core wall by 90% and 250%, respectively.

Integrity of Bolted Angle Connections Subjected to Simulated Column Removal.

Large-scale tests of steel gravity framing systems (SGFSs) have shown that the connections are critical to the system integrity, when a column suffers damage that compromises its ability to carry gravity loads. When supporting columns were removed, the SGFSs redistributed gravity loads through the development of an alternate load path in a sustained tensile configuration resulting from large vertical deflections. The ability of the system to sustain such an alternate load path depends on the capacity of the gravity connections to remain intact after undergoing large rotation and axial extension demands, for which they were not designed. This study experimentally evaluates the performance of steel bolted angle connections subjected to loading consistent with an interior column removal. The characteristic connection behaviors are described and the performance of multiple connection configurations are compared in terms of their peak resistances and deformation capacities.