Rotation Demands Research Articles

Seismic damage evaluation of a steel building using stress triaxiality

This paper presents a procedure for the evaluation of the seismic damage in steel moment frame buildings. The rotational capacities, of typical connections of a building in the Los Angeles area, which suffered extensive damage during the Northridge earthquake, were determined using stress triaxiality as an indicator for fracture. The rotational demands of the same connections were obtained from a three-dimensional finite element analysis of the building model. Comparisons of the rotational demands at several locations in the building to the rotational capacities determined by the stress triaxiality analysis showed that fracture of steel moment connections of the building are governed by the triaxiality of stresses. Based on a number of moment connections analyzed, the paper suggests a moment capacity equation for the pre-Northridge welded steel moment connections taking into account the fracture incidence due to stress triaxiality effect. The moment capacity of such connections as dictated by stress triaxiality compared favorably to FEMA-350 requirements.

Behavior and design of single plate shear connections

Steel shear connections are primarily used to transfer the reaction of a simply supported beam to its support, normally a column or a beam. Currently, the most common shear connection in North America is a single plate connection consisting of a plate fillet welded to a supporting column or girder and bolted to the web of a simply supported beam. A shear connection should be strong enough to be able to transfer the shear force, yet, it should be sufficiently flexible and ductile to allow the end of simply supported beam to rotate with ease and accommodate the rotation demand of the beam. This paper summarizes a number of research and development projects conducted at the University of California, Berkeley to study behavior of single plate shear (shear tab) connections and to develop design procedures and guidelines, both for gravity and lateral load (seismic and wind) effects. The connections were sufficiently ductile to accommodate end rotation demands of simply supported beams under gravity load and drift rotations under lateral load effects. Design procedures developed and proposed and currently used in design of single plate connections are strength-based procedures that ensure occurrence of ductile and more desirable failure modes, such as yielding of the steel plate prior to occurrence of brittle and less desirable failure modes such as fracture of bolts and welds.

Design, Specification, Installation, and Maintenance of Modular Bridge Expansion Joint Systems

Data regarding service performance and durability of modular bridge expansion joint systems were gathered through a comprehensive literature review, survey of transportation agencies, and field observations. Typical service life and desired service life targets are discussed. Maximum movement and rotation demands are given with respect to three axes. Performance and durability problems include problems that can be traced to poor design and/or installation, wear and tear of elastomeric parts, and fastener loosening and fatigue cracking of the metal parts. Fatigue cracking has been addressed in previous research. Guidance on design, detailing, specifications, installation, and maintenance is discussed, which should reduce the problems in the first group. Problems with the elastomeric parts and fasteners are best addressed through performance tests on the modular bridge joint systems as a system. Two system performance tests, an opening movement/vibration test, and a seal push-out test are suggested for the prequalification of specific modular bridge expansion joint systems.

Deformation and ductility considerations of ductile coupled shear walls located in Canadian seismic regions

This paper presents the results of an analytical study on the nonlinear deformation and ductility response of reinforced concrete ductile coupled shear walls (CSWs) under seismic loadings. The CSWs were designed, calculated, and detailed in compliance with the National Building Code of Canada (NBCC) 1995 and the Canadian Concrete Standard CAN3-A23.3-94. The parameters and assumptions of the study as well as the description of the models and the procedure were fully described elsewhere. Results indicated that the maximum interstorey drift from dynamic analyses was well below that obtained from static analyses with NBCC specified lateral forces. It was also found to be substantially lower for tall CSWs compared to short or medium-height walls, and decreased only slightly as the degree of coupling increased within the range considered in this study. It was also highest for seismic records with low PGA/PGV ratios. Plastic hinge rotations as well as accumulated plastic hinge rotations generally decreased as the number of storeys increased. The maximum displacement ductility demand factor remained below the NBCC value of 4.0 specified for ductile CSWs. The influence of degree of coupling on the maximum displacement ductility demand factor was found negligible. Also, the maximum displacement ductility demand factor generally decreased as the number of storeys increased. The maximum rotational ductility demand factor in coupling beams decreased as the number of storeys increased and was generally less than the practical accepted limit of 10, except for a few short CSWs.Key words: coupled shear walls, reinforced concrete, seismic, degree of coupling, frequency content, interstorey drift, plastic hinge deformation, ductility.

Deformation and ductility considerations of ductile coupled shear walls located in Canadian seismic regions

This paper presents the results of an analytical study on the nonlinear deformation and ductility response of reinforced concrete ductile coupled shear walls (CSWs) under seismic loadings. The CSWs were designed, calculated, and detailed in compliance with the National Building Code of Canada (NBCC) 1995 and the Canadian Concrete Standard CAN3-A23.3-94. The parameters and assumptions of the study as well as the description of the models and the procedure were fully described elsewhere. Results indicated that the maximum interstorey drift from dynamic analyses was well below that obtained from static analyses with NBCC specified lateral forces. It was also found to be substantially lower for tall CSWs compared to short or medium-height walls, and decreased only slightly as the degree of coupling increased within the range considered in this study. It was also highest for seismic records with low PGA/PGV ratios. Plastic hinge rotations as well as accumulated plastic hinge rotations generally decreased as the number of storeys increased. The maximum displacement ductility demand factor remained below the NBCC value of 4.0 specified for ductile CSWs. The influence of degree of coupling on the maximum displacement ductility demand factor was found negligible. Also, the maximum displacement ductility demand factor generally decreased as the number of storeys increased. The maximum rotational ductility demand factor in coupling beams decreased as the number of storeys increased and was generally less than the practical accepted limit of 10, except for a few short CSWs.Key words: coupled shear walls, reinforced concrete, seismic, degree of coupling, frequency content, interstorey drift, plastic hinge deformation, ductility.

Selective right parietal lobe activation during mental rotation: a parametric PET study.

Regional cerebral blood flow (rCBF) was measured with PET in seven healthy subjects while they carried out a mental rotation task in which they decided whether alphanumeric characters presented in different orientations were in their canonical form or mirror-reversed. Consistent with previous findings, subjects took proportionally longer to respond as characters were rotated further from the upright, indicating that they were mentally rotating the characters to the upright position before making a decision. We used a parametric design in which we varied the mental rotation demands in an incremental fashion while keeping all other aspects of the task constant. In four different scanning conditions, 10, 40, 70 or 100% of the stimuli presented during the scan required mental rotation while the rest were upright. The statistical parametric mapping technique was used to identify areas where changes in rCBF were correlated with the rotational demands of the task. Significant activation was found in only one area located in the right posterior parietal lobe, centred on the intraparietal sulcus (Brodmann area 7). The experimental literature on monkeys and humans suggests that this area is involved in a variety of spatial transformations. Our results contribute evidence that such transformations are recruited during mental rotation and add to a body of evidence which suggests that the right posterior parietal lobe is important for carrying out visuospatial transformations.

Seismic evaluation of an existing reinforced concrete framed tube building based on inelastic dynamic analysis

A seismic assessment of an existing 32-story reinforced concrete framed tube building is performed using inelastic dynamic time-history analysis to obtain force and deformation response of the structure subjected to three ground motion records. Details of the modeling based on the DRAIN-2D program, plastic rotation, rotation and curvature ductility demands and capacity evaluation of members are discussed. Recent recommendations for plastic hinge rotation and plastic hinge length modifications are discussed and the results of the application of some of these recommendations are evaluated. Some observations with regard to shear lag effect are presented and some of the difficulties in using the direct results of inelastic dynamic time history analysis in seismic assessment for practical applications are demonstrated.

DEFORMATION-CONTROLLED EARTHQUAKE-RESISTANT DESIGN OF RC BUILDINGS

A procedure for deformation-controlled, or displacement-based, seismic design of multistorey RC buildings is proposed, implemented and applied for the full design of a four-storey RC structure. It is integrated into the overall structural design, along with the design for the non-seismic actions and consists of a ULS verification against the conventional strain limits for a frequent “serviceability” earthquake and of proportioning the compression reinforcement and the transverse reinforcement of critical regions of members to meet the member peak inelastic chord rotation demands under the “life-safety” seismic action. Quantitative rules and expressions are proposed for the estimation of (a) mean and upper-characteristic peak inelastic chord rotation demands, through appropriate linear-elastic analyses, and (b) mean and lower-characteristic values of member ultimate chord rotations, in terms of member geometric and material data.

Classification of damage to steel buildings observed in the 1995 Hyogoken-Nanbu earthquake

This paper presents an overview of the damage to steel buildings observed in the 1995 Hyogoken-Nanbu earthquakes. It summarizes the Japanese seismic design concept and the level of earthquake forces exerted on steel buildings built in severely shaken regions. Statistical data on the damage are presented with respect to the building height and type and the location of damage and typical damage is highlighted. The damage to welded beam-to-column connections is explained from the perspectives of materials, welding, connection details and plastic rotation demand. Finally, the damage was classified with respect to the previous awareness and the difficulty in providing solutions.

System seismic performance of haunch repaired steel MRFs : dual panel zone modeling and a case study

Recent test results of steel moment connections repaired with a haunch on the bottom side of the beam have been shown to be a very promising solution to enhancing the seismic performance of steel moment-resisting frames. Yet, little is known about the effects of using such a repair scheme on the global seismic response of structures. When haunches are incorporated in a steel moment frame, the response prediction is complicated by the presence of panel zones. To investigate the effects of a repair on seismic performance, a case study was conducted for a 13-story steel frame damaged during the 1994 Northridge earthquake. It was assumed that only those locations with reported damage would be repaired with haunches. A new analytical modeling technique for the dual panel zone developed by the author was incorporated in the analysis. Modeling the dual panel zone was among the most significant consideration in the analyses. Both the inelastic static and dynamic analyses did not indicate detrimental side effects resulting from the repair. As a result of the increased strength in dual panel zones, yielding in these locations were eliminated and larger plastic rotation demand occurred in the beams next to the shallow end of the haunches. Nevertheless, the beam plastic rotation demand produced by the Sylmar record of 1994 Northridge earthquake was still limited to 0.017 radians. The repair resulted in a minor increase in earthquake energy input. In the original structure, the panel zones should dissipate about 80% (for the Oxnard record) and 70% (for the Sylmar record) of the absorbed energy, assuming no brittle failure of moment connections. After repair, the energy dissipated in the panel zones and beams were about equal.

Lateral-Load Response of Two Reinforced Concrete Bents

Two reinforced concrete bridge bents were subjected to large, transverse displacements. The bents contained detailing deficiencies typical of the 1960s, including minimal transverse reinforcement, short reinforcing splices, and a lack of top reinforcement in the footings. Spalling of the concrete cover at the column tops began at a drift ratio of 1.5. At this drift ratio, the column displacement ductility was approximately four, the curvature ductility was eight, and nominal curvature in the plastic hinges corresponded to a nominal maximum concrete strain of 0.01. In spite of their deficiencies, the bents resisted transverse loads equal to nearly 40% of the bridge's weight at a drift ratio of 3%. The ductile response was attributed to a low shear demand and to the influence of the soil in redistributing the rotational demands away from the column splices. The measured response was reproduced well by an analytical model that considered the nonlinear force-deformation relationships of the columns and soil. The results of a parametric study indicated that the soil surrounding the column bases increased the column shear demand by 25%.

構造物に要求される消費エネルギーに対して構造各部材に要求される塑性変形量とそのばらつきの評価法

This paper presents a simple procedure to obtain variation of plastic rotation demand for a given energy to be dissipated by a structural system. Plastic rotations of individual plastic hinges are computed as the sum of the rotations to be given before the system reaches its failure mechanism and the rotations to be given during the rigid body motion, and their variation is estimated from the first order approximation. It is found that (1)the proposed procedure is effective when the energy demand is not large and (2)the variation of plastic rotation demand increases when various failure modes are likely to occur and when larger energy demand is specified. It is pointed out that to ensure the failure mechanism specified in design is the key to control the plastic rotation demand.

Seismic Response of Flexibly Supported Coupled Shear Walls

Results from seismic analyses performed on 20-story ductile coupled-shear-wall models designed for Montreal, Canada, are presented. A two-dimensional model was used to idealize the structure including the supporting ground. Allowances were made for nonlinearities not only in the walls and the coupling beams, but also in the soil and foundation elements. The soil foundation was modeled by equivalent massless springs (hangers), located at the base of the structures, allowing for inelastic bearing of the soil and loss of contact (uplift) of base from supporting soil. The stiffnesses of massless foundation springs were obtained using the soil properties that were derived on the basis of strain-dependent shear moduli of real borings. The study showed that the model is capable of tracing the response of coupled shear wall, taking into account the soil-structure interaction effects. Results showed that allowing for foundation flexibility lengthened the fundamental period by a maximum of 33; it amplified deflections by a maximum of 81. However the stresses in the walls and the coupling beams attenuated particularly in lower stories. Finally, no substantial variations were observed in the rotational ductility demands of the coupling beams.

Patterns of cerebral activation while mental images are rotated and changed in size

Event-related brain potentials were recorded while subjects performed either a rotation or a size scaling transformation of a mental image. Images had to be rotated 0 degrees, 60 degrees, or 120 degrees or their size had to be enlarged by factors of 1:1, 1:3, or 1:5. Both tasks were accompanied by pronounced negative slow potentials, which extended over several seconds. The relative maximum of these shifts emerged at central to occipital leads. Over the occipital cortex, the negative potential had a similar amplitude level in all conditions and both tasks. However, at parietal and central areas, the negative slow wave changed in relation to the difficulty of the task. The amplitude increased with increasing rotation demands and if the scaling operation required an exact computation of the coordinates of the image. None of these effects could be attributed to an inverse change of P300.

Seismic performance of moment resisting frames with flexible joints

An analytical study was conducted to investigate the effect of joint flexibility, in particular extended end-plate joints, on the response of moment resisting frames. Eight storey frames having extended end-plate joints and with joints detailed according to different design criteria, were analysed for different earthquake records using a step-by-step time history analysis. Realistic models developed from an extensive experimental research program were used to simulate the joint response. An evaluation of the frames' performance in terms of lateral deflection, inter-storey shear, drift, and the inelastic rotational demands imposed upon the beams, columns and joints was carried out. It is concluded that joint behaviour is an important consideration in a frame's response. Also, its performance can be much improved by properly designing and detailing the joints.

Inelastic Limit States Design Part II: Three‐Dimensional Frame Study

A design study of a three‐dimensional 22‐story frame is presented to demonstrate the use of second‐order inelastic analysis in load and resistance factor design. This study is a follow‐up to a set of low‐rise planar frame studies presented in a companion paper. The limit state behavior of the inelastic design is evaluated with respect to strength and serviceability requirements. The strength requirements include investigating the inelastic rotation demands, effects of residual stresses, and conformance with a limit states design specification. The inelastic design is also compared to a design obtained using conventional elastic methods of analysis. The study indicates that with computer‐aided engineering, second‐order inelastic analysis provides a feasible alternative for designing steel structures of substantial size. It also concludes that existing limitations of current analytical techniques, e.g., the inability to model torsional‐flexural instabilities of beam‐columns, need to be overcome before inelastic analysis‐design approaches such as that presented can be generally applied.

Seismic behaviour of a reinforced concrete portal frame sustaining gravity loads


 
 
 
 To study the behaviour of multistorey building frames under gravity and severe earthquake conditions a reinforced concrete portal frame was constructed. The beam was subjected to constant vertical loads while a cyclic lateral load was applied to the unit. Negative moment plastic hinges formed at the column faces while the positive moment hinges were located in the span. The rotations generated by each inelastic displacement accumulated. This placed high rotational demands on the plastic hinges, which reduced the overall ductile behaviour compared with that observed in typical beam-column sub-assembly tests. The high rotations caused the beam to grow in length.
 
 
 

The Mexico Earthquake of September 19, 1985—Analysis of the Seismic Performance of a Medium Rise, Waffle Flat Plate Building

This paper analyzes the seismic performance of a 15-story waffle-flat plate building affected by the September 19 Mexico earthquake. It also evaluates the adequacy of present analytical methods for predicting observed damage and response. In addition, it proposes a model to define the supplied slab seismic strength for nonlinear analysis. Results from this analysis correlate reasonably well with the observed seismic behavior of the building. Particularly, distribution of computed maximum rotational ductility demands on slabs agree well with observed maximum slab damage in the building.

Demand and supply of ductility in steel shear connections

Abstract Major response characteristics of shear connections are discussed. Interactions of the shear force, bending moment and rotation are discussed. The beam line concept is refined to include the inelastic range of behavior of the beam. The refined inelastic beam lines are recommended to be used in predicting rotational ductility demand of steel connections under service as well as ultimate load conditions. Inelastic responses of a large number of simply supported beams were analyzed and by using the results, a mathematical model was developed to predict rotational ductility demand of the steel shear connections. Some common test procedures which have been used by several investigators in the past to measure strength or stiffness were evaluated. It is shown that these procedures do not properly simulate the actual conditions in a shear connection. A new test procedure is proposed and was used to measure response characteristics of single-plate, tee and double-angle shear connections more realistically than current procedures.

Earthquake Load on R/C Beams: Building versus Single Beam

The results of a series of tests on a full-scale reinforced concrete structure subjected to simulated earthquake loading are used to study the behavior of beam hinging regions. The measured beam rotations from an open frame and a shear wall frame are compared to the results from an analytical study to estimate the rotational ductility demand of beams at different stages of building displacement. The results indicate that there is a pronounced difference between the ductility demand of beams in an open frame and those connected to a shear wall. A relationship between the beam hinge rotation of the actual structure and displacements of individual beam elements is presented to establish a guideline for choosing displacement histories for experimental programs of beam elements. The analysis shows that there is not a unique relationship between the displacement of individual beam specimens and the lateral displacement of the building, nor is this relationship linear. The specimens that simulate the behavior of beams at different locations in a building should undergo different displacements histories.