University of Illinois Contribution on Analytical Investigation Amr S. Elnashai Sung Jig Kim Curtis Holub Narutoshi Nakata Oh Sung Kwon

Outline  Introduction  Analysis Tools  Effect of Vertical Ground Motion on Piers  Assessment of Bridge with Skewness Considering Torsional Effect on RC Piers  Advanced Bridge Analysis with Soil-Structure Interaction  Future Work

Introduction

Analytical Focus  Analysis of a series of bridge structures subject to different levels of earthquake excitations –DIANA, OpenSees, and Zeus-NL- the MAE Center advanced analysis platform –The unique features of each FE application will be combined as distributed computational simulation using UI-SIMCOR as a simulation coordinator –Analytical work will provide the modeling of PSD conditions to zoom on parameters resulting in high levels of simultaneous horizontal and vertical accelerations.  Study the seismic response of the bridge systems, including foundations and surrounding soils –Appropriate multidirectional loading and boundary conditions for columns can be obtained  Determination of the appropriate input loading for the specimens tested in the subsequent phases of the project

Analysis Tools

 FE applications Nonlinear frame analysis, nonlinear hysteretic concrete model, meshed section, freely available Open source application, soil modeling 2 and 3-D modeling of reinforced concrete structures  UI-SimCor –Simulation coordinator for the distributed computational simulation –Combine unique features of each application Analysis Tools

UI-SimCor  Simulation overview Tested Structure UI-SIMCOR Disp. Force Soil & Foundation Module (OpenSees) Disp. Force Structural Module (Zeus-NL) Multi-Platform Simulation Framework  Key components of implementation –PSD test integration scheme: α-OS method –Sub-structuring technique –Communication between each modules –Hardware for physical testing

UI-SimCor API Equipments Component n Simulation Coordinator Component 1 MDL 1 Object 1 of MDL_RF class Simulation Monitor Client DOF Mapping MDL n Object n of MDL_RF class Simulation Monitor Client AUX Objects of MDL_AUX class Client Stiffness Evaluation Static Equilibrium Dynamic Equilibrium Simulation Control Main Routine Disp. Force DAQ Camera TCP/IP Network Server API  Framework architecture Multi-Platform Simulation Framework

Effect of Vertical Ground Motion on Bridge Pier

Parametric Study with Simple Model  Parameters –Five equal spans with each span length varying 10m to 50m –Variable span (5 cases): The ratio of the length of first span to that of second span is changed from 0.2 to 1.0 –Variable column height (5 cases): 4 m to 12 m  Ground motions recorded at 6 stations  6 combinations of components for each EQ record –L, T, L+T, L+V, T+V and L+T+V –L: longitudinal GM, T: Transverse GM, V: Vertical GM H L2L1 Pier Section

Parametric Study with Simple Model  Axial force is mainly affected by vertical ground motion –Especially, as span ratio increase, the effect of vertical seismic motion to axial force increase significantly only when vertical record is considered  Shear capacity is reduced by vertical ground motion –Span length is longer –Span ratio is close to 1 –Column height is shorter –In case of seismic assessment for the structure with above geometric configurations, vertical ground motion should be considered Axial force Axial force variation HGM VGM Increasing ratio of V due to VGM V due to VGM Summary

Complex Straight Bridge  Prototype Structure –Collector-Distributor 36 of the Santa Monica (I10) Freeway –Significant damage by Northridge earthquake (1994)  Model Structure –The bridge is assumed to have three piers –The initial loads applied to the top of piers as deck self-weight  6 earthquake records used in parametric study were selected Expansion Joint Rectangular Wall (B=457, H=9000) Circular Pier (D=1219) Layout of Santa Monica Freeway (unit, mm) m m m m m m m Layout of Model Structure Pier 1 Pier 2 Pier 3 Initial load #4 406mm cs. 24-#11 for the outer bars 8-#11 for the inner bars Total: 32 - # mm 50.8mm cover Concrete Concrete -, Reinforcement bar Reinforcement bar -, - Initial load (kN) Modeling and Consideration

Complex Straight Bridge Period change by V/H ratio Vertical period of vibration Horizontal period of vibration  Variable V/H ratios –A fixed time interval and PGA of horizontal ground motion –16 V/H ratios per earthquake record are considered Range of 0.5 to 2.0 with an increment of 0.1  Effect on the periods of vibration –The period is elongated for both components as the vertical amplitude increases –The slope of rate of period increase is steeper up to a V/H Ratio of 1.0  Effect on Axial Force and Shear Capacity –Axial force variation increases as V/H ratio increases –Shear capacity is reduced by 5% to 36% Increasing ratio of shear capacity by VGM Contribution of VGM to axial force variation Effect of V/H Ratio

Horizontal period of vibration, Kobe (port Island) Complex Straight Bridge  Variable time interval –Range 0.0 to 5.0 sec with an increment of 0.5 sec (11 cases) –This is accomplished by shifting the HGM along the time axis –The original recorded V/H ratios are fixed  Effect on the period vibration and Shear Capacity –The horizontal period is more elongated when the time interval is small –The shear capacity tends to increase slightly as the arrival time interval increases Increasing ratio of capacity by VGM Effect of Time Interval

Torsional Effect on Bridge Pier

Proto-type Bridge FHWA No.4 Skew Bridge (FHWA-SA , 1996)

Parametric Study with Various Skew Angles 1 st Mode: Longitudinal F 1 : 1.99 (Hz) 2 nd Mode: Transverse F 2 : 2.40 (Hz) 3 rd Mode: Rotational F 3 : 2.96 (Hz) 4 th Mode: Bending F 4 : 3.34 (Hz) Fundamental Vibration Modes Parametric Skew Angles

Effect of Skew on Natural Frequencies  Up to 30 degree, effect of skew angle is slightly small on the fundamental frequencies.  Effect is more significant on deck bending modes than any other modes.

Parametric Study with Span Length Ratios Symmetric Span Ratios Asymmetric Span Ratios Parametric Model Span Length Configurations

Effect of Span Length Ratios  Rotational and Bending modes are sensitive to the variation of span length ratios.  Effect of the skew angle in any span length ratio configuration are negligible on the natural frequencies.

Effect of Span Length Ratios Symmetric Span RatiosAsymmetric Span Ratios Torsional / Transverse Ratio in Transverse Mode  In symmetric span length configurations, torsional effect on any piers are somewhat similar regardless of skew angle.  With skew angle and asymmetric span length configuration, torsional effect in fundamental modes can be significantly different depends on the location of the piers. Torsional effect is higher than any other piers in any configurations. Torsional Effect on RC Piers

Selection of Bridge Configurations 1/1.2 1 Case 1 Skew Angle: 0 (degree) Span Length Ratio: 1/1.2 : 1.0 : 1/1.2 1/1.2 1 Case 2 Skew Angle: 30 (degree) Span Length Ratio: 1/1.2 : 1.0 : 1/1.2 Case 3 Skew Angle: 30 (degree) Span Length Ratio: 1/1.2 : 1.0 : 1/2.0 1/ /1.2  In order to see the effect of skew angle, two bridge configurations, straight and 30 degree skew angle, are selected for further detail study.  For the evaluation of extreme torsional effect within regular bridge category, configuration with span length ratio, 1/ /1.2, is also selected for further study.

Advanced Bridge Analysis with Soil-Structure Interaction

Advanced Bridge Analysis with SSI  Effect of soft soil deposit on structural response –Ground motion amplification –Structural period elongation –Radiational and hysteretic damping –Permanent soil deformation Bedrock Soft Soil –SSI, detrimental or beneficial. … ? –Displacement redistribution –Force redistribution –Input motion change  Neglecting SSI can be highly inaccurate Background

Introduction – MRO Bridge  Meloland Road Overcrossing Bridge

Introduction – MRO Bridge  Recorded Ground Motions ID Date yr/mo/dy MLLatLongDepth (km)Epic. Dist. (km)PGA (g)Available record 1 GM0179/10/ B GM0299/10/ D GM0300/04/ B, D GM0400/06/ B, D GM0500/06/ B, D GM0602/02/22N/A 0.039B, D Note 1. B: Bridge array records, D: Downhole array records

Pile Foundation Model  Material properties and FE model geometry Medium clay G = 60 MPa, B = 300 MPa, Cohesion = 35.9 kPa, ρ = 1.5 t/m 3 Stiff clay G = 150 MPa, B = 750 MPa, Cohesion = 76.6 kPa, ρ = 1.8 t/m 3 Medium sand G r = 75 MPa, B = 200 MPa, = 33°, P r = 80 kPa, ρ = 1.9 t/m 3 Stiff clay G = 150 MPa, B = 750 MPa, Cohesion = 86.2 kPa, ρ = 1.8 t/m 3 Medium sand G r = 75 MPa, B = 200 MPa, = 33°, P r = 80 kPa, ρ = 1.9 t/m 3 0 m m m m m m m m m m Concrete pilecap Timber piles E = 2480 MPa, v = 0.2. E = 1240 MPa, v = m y z 17 m x

Embankment-Abutment Model  FE Model Geometry and Material Properties Medium clay G = 60 MPa, B = 300 MPa, Cohesion = 35.9 kPa, ρ = 1.5 t/m 3 Gravely clay G = 19 MPa, B = 90 MPa, Cohesion = 20 kPa, ρ = 1.6 t/m 3 (Vs = 110 m/sec, v = 0.4) Stiff clay G = 150 MPa, B = 750 MPa, Cohesion = 76.6 kPa, ρ = 1.8 t/m m m 0.0 m -7.5 m 7.9 m -60 m45 m0.0 m Concrete abutment Timber piles E = 2480 MPa, v = 0.2. E = 1240 MPa, v = 0.2 x z

Multi-Platform MRO Bridge Model Note: Dimension of bridge is exaggerated. x y z Mass defined in UI-SimCor Structural model in Zeus-NL Geotechnical model in OpenSees  System configuration

Multi-Platform MRO Bridge Model T 1 = sec Ch 26Ch 13Ch 9Ch 7Ch 5Ch 3Ch 11  System identification from recorded ground motions and comparison with analytical model

MRO Bridge Analysis with SSI  Damping evaluation from GM03 Maximum response Subsequent peaks from near-free vibration Impact-type earthquake loading

MRO Bridge Analysis with SSI  Time history analysis and comparison with recorded motion

Summary  The MRO Bridge, which was heavily instrumented and studied, is modeled with two analysis platforms.  Each components of the soil-foundation-bridge system is verified through comparison with previous researches  Multi-Platform analysis is applied to combine two different platforms.  The modal properties is close to the properties identified from measured records.  The time history analysis result showed good correspondence with measured records.

Future Work

 FHWA No. 4 Bridge was selected as the prototype for experimental investigation –Using Zeus-NL with strong motion records, the effect of vertical ground motion on bridge pier will be investigated –2~3 strong motion records will be selected from the analyses above –Loading protocol from analyses will be provided to pier analysis with DIANA for more extensive analysis Selection of Strong Motion Records and Loading Protocol

Future Work  The selected loading protocol will be verified using DIANA  Using UI-SimCor, the computational simulation will be conducted –Deck will be simulated using Zeus-NL –Piers will be analyzed using DIANA  The obtained result will be provided to experimental investigation Verification by DIANA and Computational PSD simulation

Thank you & Questions?