s pecial dition apercolumn with the large beam at a right angle to the double girder. in this...
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39JR EAST Technical Review-No.26
Special edition paper
From a perspective of effective use of over-track space, we proposed a frame form that secures installation space for seismic isolation devices such as laminate rubber and dampers while reducing the seismic isolation layer height as much as possible.1) We carried out structural tests using scaled-down models of the structure around that seismic isolation layer. And based on the test results, we further proposed a design method and verified the validity of that method.
Overview of Frame Form2Fig. 1 shows a frame form where a seismic isolation construction method is employed for an aboveground two-story building (first level: track level, second level: concourse level, hereafter “assumed building”) having an upper structure of pure steel rigid frame structure. This was designed as a mid-story isolated building where a seismic isolation layer was set up directly above the track level so as to prevent displacement of the seismic isolation layer from interfering with train operation on the track level and passenger flow on the platforms. In order to secure overhead clearance of the track level so as to not obstruct clearance gauge, the seismic isolation layer was of a form where its lower beam, which is ordinarily straight, was bended upward. The upper beams of the seismic isolation layer were replaced with two large beams (hereafter “double girder”). By placing the bent lower beam between the beams of the double girder, the height of the seismic isolation layer was reduced while securing space for the damper.
In such details, the double girder is not fixed to the column directly above the seismic isolation layer; instead, it fixed to the column with the large beam at a right angle to the double girder. In this structure, the double girder cannot transfer the applied bending moment as the torsional resistance of the perpendicular large beam to the column because the double girder cannot directly transfer that bending moment to the column. Therefore, in order to confirm the structural performance of the part around
Introduction1
the seismic isolation layer, we carried out static loading tests using a scaled-down specimen that reproduced the part shown in Fig. 1.
Outline of Tests33.1 Overview of the SpecimenFig. 2 shows the shape and dimensions of the specimen modeling the frame form of the upper seismic isolation layer. The 1/1.6-scale specimen modeled the seismic isolation layer and its upper column up to its point of contraflexure and its beams at the both ends also up to their points of contraflexure. The column was 300 × 300 × 16 mm square (STKR400), the beam directly fixed to the column was a 400 × 200 × 8 × 13 mm H-beam (SS400), and the double girder fixed to the column with the large beam was 500 × 200 × 10 × 16 mm H-beams (SS400). The laminate rubber was seismic isolation and vibration control laminate rubber (RV30 - 520 - 27.2 × 3), of which lower surface was supported in a secure manner.
Research on Structural Performance of Frame Forms in Seismic Isolation and Vibration Control of Over-track Buildings
•Keywords: Over-track building, Seismic isolation, Laminate rubber, Static loading test
Past research suggests the possibility that employing seismic isolation technology could reduce response of a building in an earthquake and accordingly allow for smaller lower structures. JR East has also proposed jointly with Takenaka Corporation a frame form called “double girder form.” The aim of that form is to secure clearance gauge at the track level in over-track spaces, which have much design and construction constraints, and at the same time to minimize the space required for the seismic isolation layer. In this research, we conducted static loading tests using a scaled-down specimen consisting of laminate rubber and a double girder so as to clarify the structural performance of the double girder. By simulating the test results, we established a design method for double girders.
*Frontier Service Development Laboratory, Research and Development Center of JR East Group
Madoka Yamataka* Tsutomu Hoshikawa*
Scope modeled
倉庫
北口歩道レベル
基準RL
基準HL
最高高さ
下り線
上り線
ホーム
(a) Cross-sectional view
(b) Detailed planar view (c) Perspective drawing of frame form
Seismic isolation layerupper beams (double girder)
Seismic isolationlayer lower beam
Seismic isolation layer
Laminate rubberUpper beam
Lower beam
Upper beam
Fig. 1 Overview of Seismic Isolation of an Over-track Building
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40 JR EAST Technical Review-No.26
Special edition paper
We controlled the load by shear deformation angle of the laminate rubber, and we applied positive and negative progressive loads twice at each of shear deformation angles of +/-50%, +/-100%, +/-150%, +/-200%, +/-250%, and +/-300%. Here, shear deformation angle 300% is about 1.2 times larger than the maximum shear deformation angle of the laminate rubber that can be obtained from the seismic response analysis in the case where Level 2 seismic vibration specified in the railway aseismic standard2) was applied to the assumed building.
3.3 Measurement MethodWe measured the horizontal displacement of individual parts of the seismic isolation layer of the specimen using a retractable displacement gauge, and we measured the angle of gradient of the upper surface of the laminate rubber using a clinometer. We also measured the deformation angle between the layers of the upper frame and the torsion angle of the perpendicular beam.
We further measured the strain near the joint of the ends of the double girder and the beam and the strain caused by the torsion of the perpendicular beam to which the double girder was fixed. The bending strain at the ends of the beam directly fixed to the column and the bending strain and axial strain of the column were measured too.
Test Results4This article covers the test results of Patterns 1 and 3 from Patterns 1 to 4. Fig. 5 shows the relation of horizontal force and deformation angle between layers for the whole frame as deformation in the range from the lower end of the laminate rubber to the loading point. Fig. 6 shows the relation of horizontal force and laminate rubber shear strain, and Fig. 7 shows the relation of horizontal force and deformation angle between layers of the upper frame. To the +/-300% amplitude of the shear strain of the laminate rubber, both of the laminate
Table 1 lists the tested patterns. The four parameters were the position of the column (center column or side column) and the span of the double girder (short or long). In the case of a center column, the beam fixed directly to the column was assumed to be supported by a pin and roller, and in the case of a side column, free ends were to be supported by the pin and roller. The span length of the double girder was determined by the position of the pin-roller support on the double girder.
Table 2 shows the mechanical properties of the steel material used for the specimen.
3.2 Loading MethodFig. 3 shows an overview of the force applicator. In design of the assumed building, we applied to the column of the specimen using a hydraulic jack axial force equivalent to the average surface pressure of the laminate rubber (269 kN, excluding deadweight), and we also applied horizontal load at the point of contraflexure of the column. As the point of contraflexure of the beam was a pin-roller support, it gave resistance to vertical force only. By measuring that vertical force using a pin-type load cell, we calculated the bending moment that acted on the beam.
Fig. 4 shows the appearance of the whole specimen and force applicator and the state of the laminate rubber after applied with the axial force (269 kN).
Linear slider
Pin-type load cell
Seismicisolator ø520
Pin-type load cell
Linear sliderLinear slider
Vertical jackHorizontal jack
Upper frame form
Pin-roller support point
Column: 300 × 300 × 16 mm square
Pin-rollersupport point
Double girder: 500 × 200 × 10 × 16 mm H-beams
Elevation view
Planar view
Laminate rubber ø520
Double girder: 500 × 200 × 10 × 16 mm H-beams
σ ε μ σ εPart Steel type
Degree ofyield stress Yield strain Tensile strength Yield ratio Elongation
Column
Panel
16 mm
19 mm
22 mm
19 mm
9 mm
12 mm
32 mm
Double girder500 × 200 × 10 × 16 H-beams
Beam400 × 200 × 8 × 3 H-beam
Upper diaphragm
Lower diaphragm
Large beam web
Reinforcement rib
Seismic isolation layer joint
Diameter orplate
thickness
Table 2 Mechanical Properties of the Steel Materials
Fig. 4 Overall View of Specimen (left),Laminate Rubber after Applying Axial Force (right)
Fig. 3 Overview of the Force Applicator
Fig. 2 Overview of the Specimen
Test pattern Double girder span Column positionLongShortLongShort
1234
Center column
Side column
Table 1 Test Patterns
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41JR EAST Technical Review-No.26
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rubber and the upper frame form largely expressed elastic behavior.
Fig. 8 shows the relation of horizontal force and laminate rubber angle of gradient. This shows largely elastic behavior, while the rigidity varied depending on whether it as positive or negative. The reason for the difference in rigidity would be because the horizontal deformation of the laminate rubber increased the vertical downward displacement of the upper laminate rubber and additional stress was generated there. Fig. 9 is a photo of the deformation in Pattern 1 at a laminate rubber shear deformation angle of +300%.
Examination of the Design Method5When designing a double girder frame by replacing members with straight materials as usually done in designing a rigid frame structure, we have to take appropriate account of torsional deformation at joints generated due to the double girder beam ends and the column not being directly fixed to each other. In this chapter, we will propose a modeling method for replacing the double girder frame with straight members and verify the validity of that method by simulating the test results.
5.1 Proposing a Simulation ModelOur policy in modeling is (1) to model two beams of the double girder as one beam, and (2) to model the effects of the torsional deformation at joints as rotational springs (Fig. 10).
In order to model two beams of the double girder as one beam, we double the specifications of each cross-section of the beam.
In terms of torsional deformation at joints, we assume that bending torsion—so-called Wagner torsion—would stand out because the cross-sectional shape at joints is similar to that of a H-beam (Fig. 11).
Laminate rubber angle of gradient (degree) Laminate rubber angle of gradient (degree)
Pattern 1 Pattern 3
(Center column, span 4 m) (Side column, span 4 m)
Boundary conditions di�erent between both ends of the torsion sectionCross-section of
torsional resistance:�ickness di�erent between upper and lower �anges Torsion span
Fig. 8 Relation of Horizontal Force andLaminate Rubber Angle of Gradient
Deformation angle between layers R (1 / 1000 rad.) Deformation angle between layers R (1 / 1000 rad.)
Pattern 1 Pattern 3
Laminate rubber shear strain (%) Laminate rubber shear strain (%)
Pattern 1 Pattern 3
(Center column, span 4 m) (Side column, span 4 m)
(Center column, span 4 m) (Side column, span 4 m)
Deformation angle between layers R (1 / 1000 rad.) Deformation angle between layers R (1 / 1000 rad.)
Pattern 1 Pattern 3
(Center column, span 4 m) (Side column, span 4 m)
Fig. 5 Relation of Horizontal Force andDeformation Angle Between Layers for Whole Frame
Fig. 7 Relation of Horizontal Force andDeformation Angle Between Layers for Upper Frame
Fig. 6 Rubber of Horizontal Force and Laminate Shear Strain Relation
Column
Large beamModeling of two large beams replaced with one straight member
Rotational springstaking into account torsional deformation at joints
Replacing withstraight materials
Fig. 10 Concept Image of Replacing Double Girderwith Straight Members
Fig. 11 Details of the Joint
Fig. 9 Photos of Deformation(Pattern 1, Shear deformation angle +300%)
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42 JR EAST Technical Review-No.26
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From the bending torsion constant EIw, rotational spring rigidity KT is derived as follows. tf is the average of the upper and lower flange thickness, and the boundary condition at the ends is pinned support.
KT = 48EIw /L3
EIw = t fb3h2 / 24 E: Young’s modulus of steel materialh: Beam depth b: Beam width L : Torsion spantf: Flange thickness (average of the upper and lower flanges)
5.2 Verification of the Validity of the Simulation ModelAs torsional deformation at joints is a problem related only to the upper frame form, we will examine only the upper frame excluding the laminate rubber. We will consider the joints as a rigid body.
To be consistent with the specimen dimensions, we set members to be 300 × 300 × 16 mm square for the column, 400 × 200 × 8 × 13 mm H-beam for the left large beam, and two 500 × 200 × 10 × 16 mm H-beams for the right large beam. The analysis program used is Nastran.
Fig. 13 shows a comparison of the test and analysis results of the horizontal force-deformation angle between layers relation. With Pattern 1, the test results agree well with the analysis results, while with Pattern 3, those agree well with each other on the side with positive loading but largely vary on the side with negative loading. Assuming the column as a side column, the position of the column-beam joint is opposite the point of pinned support from the viewpoint of the laminate rubber at negative loading. We believe that reduces rotational force of constraint, and consequently deformation progresses.
Fig. 14 shows the relation of the deformation angle between layers and the moment generated at the beam ends. As the test results for Pattern 1, we adopt data where the additional moment is corrected considering vertical rigidity of the laminate rubber lowering at an earthquake. The figure shows that the simulation results using the proposed model largely agree with the test result.
Fig. 15 shows the relation of deformation angle between layers and bending moment before adjustment. As shown in Fig. 16 (a), the effective load support part of the laminate rubber decreases, and that reduces its vertical rigidity at horizontal deformation. In such a case, the vertical deformation at the laminate rubber increases, but vertical deformation at each support point does not. Therefore, the stress shown in Fig. 16 (b) occurs. Adjustment of that bending moment leads to the relation of deformation angle between layers and bending moment as shown in Fig. 15.
Conclusion6In order to identify the structural performance of the double girder frame form around the seismic isolation layer devised for seismic isolation of over-track buildings, we carried out static loading tests using a scaled-down specimen. And we proposed a simulation model for designing double girders. The simulation results for the tests largely agree with the results of actual tests, so we could confirm the validity of the proposed model.
Reference:1) Madoka Yamataka, Kazuaki Iwasaki, Tsutomu Hoshikawa, Mitsuru
Shimizu, “Development of Low-rise Over-track Buildings Using Thick Laminate Rubber Seismic Isolation Materials”, JR East Technical Review, No. 21 (2011): 15 - 21
2) Railway Technical Research Institute, “Design Standards for Railway Structures and Commentary (Seismic Design)”, Railway Technical Research Institute
Test
Analysis
Test
AnalysisHor
izon
tal f
orce
Q[k
N]
Hor
izon
tal f
orce
Q[k
N]
Deformation angle between layers R [1/1000 rad.] Deformation angle between layers R [1/1000 rad.]
Pattern 1 Pattern 3
Test
Analysis
Test
Analysis
Bend
ing
mom
ent [
kN ·
m]
Bend
ing
mom
ent [
kN ·
m]
Deformation angle between layers R [1/1000 rad.] Deformation angle between layers R [1/1000 rad.]
Pattern 1 a�er Adjustment Pattern 3
Fig. 13 Relation of Horizontal Force andDeformation Angle Between Layers for the Upper Frame
E�ective load support part(a) Load support part of
laminate rubber
Simpli�edstructure diagram
Momentdiagram
(b) Pattern diagram of added moment
Test
AnalysisBend
ing
mom
ent [
kN ·
m]
Deformation angle between layers R [1/1000 rad.]
Pattern 1 before correction
Fig. 15 Relation of Deformation Angle Between Layers and
Bending Moment at Beam Ends
Rigid range Rotational spring
Fig. 12 Model Image of Replacement with Straight Members
Fig. 16 Concept Image of Laminate Rubber
Fig. 14 Relation of Deformation Angle Between Layers andMoment at Beam Ends (total of the values at the double girder
beams on the right of the model image)