What is the thickness of the pile cap?
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2 m.
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What is the thickness of the pile cap?
2 m.
What type of soil cover is above the pile cap?
1.5 m.
Why might ductile piers be more economical and safer for critical bridges?
They can dissipate input energy more efficiently through rotation associated with plastic hinges.
What should be conducted for bridges in SDC B?
Seismic analysis and a displacement demand to capacity check.
What design strategy does ductile design employ to avoid brittle shear failures?
Capacity design strategy.
What aspect ratio indicates susceptibility to flexural-shear failure in piers?
Aspect ratios not exceeding 3.0.
What factors are used to establish the four Seismic Design Categories?
Seismic risks and horizontal response spectral acceleration coefficient at a period of 1.0 sec.
How does the intended behavior of a bridge affect foundation design?
It affects the magnitude of seismic actions transmitted to the foundation.
What can unbalanced stiffness between columns in a pier cause?
More damage to the stiffer column due to torsion generated by rigid body rotation.
What are the two categories of normalized axial forces studied for bridge piers?
0.066 and 0.093.
Why is designing for elastic behavior often considered wasteful?
Because it should not be accepted in most cases.
What type of connection does the pier have to the deck?
Monolithic connection.
At what aspect ratio is a pier prone to shear failure under limited ductile behavior?
An aspect ratio as small as 1.7.
How does SDMHR 3rd differ from SDMHR 2013 in terms of seismic design?
SDMHR 3rd assumes elastic resistance to seismic action, while SDMHR 2013 requires ductile or limited ductile behavior.
How does pier height affect seismic design moments?
Different pier heights can influence the design moments required for seismic resistance.
What does SDC A indicate regarding the 1-sec period design spectral acceleration coefficient?
It is assigned when the coefficient is smaller than 0.15.
What is the recommended maximum skew angle for bridge design?
Less than 30 degrees if possible.
What is the range of clear height for the bridge piers studied?
From 5 m to 17 m.
What is the purpose of the Seismic Design Category (SDC)?
To determine different requirements for analysis methods and column design details.
What are the desirable characteristics for bridges to perform better during earthquakes?
Clear and dependable earthquake resisting system, reliable articulation, and balanced stiffness, mass, and strength.
What is the relationship between shear strength and displacement in bridge columns?
Base shear force and displacement at the top of the column are related to shear strength.
Why are shorter piers generally subjected to strong seismic motions?
Due to their short periods.
What happens to the tributary mass of the deck when the articulation changes to integral?
The tributary mass is halved.
What are the horizontal subgrade reaction values for Ground Types B, C, and D?
17.6 MN/m³ for B, 6.6 MN/m³ for C, and 2.2 MN/m³ for D.
What limits the lateral load capacity of a pile?
The lesser of the maximum resistance offered by the soil or the ultimate structural resistance of the pile.
What is the effect of designing a pier for ductile behavior compared to elastic behavior?
The design moment can generally be reduced significantly.
What is the significance of Importance Class I and Ground Type A in seismic design?
They indicate specific design criteria for seismic performance.
When is it preferable to design a bridge for ductile behavior?
In cases of moderate-to-high seismicity.
What is the importance of the pier height in seismic design?
It influences the design requirements and reinforcement ratios.
What is generally not required for bridges in SDC A due to low seismic hazard levels?
Seismic analysis.
What is the preferred strategy to achieve a continuous deck in bridge design?
Using continuous or integral construction.
What may apply to bridges in SDC C and above?
More stringent detailing rules.
What must be verified for the piles in bridge foundations?
They must have sufficient axial and lateral resistances.
What is the height of the bridge pier?
9 m.
What is the maximum clear distance between longitudinal bars in a pile?
Should not exceed 200 mm.
What is the normalized axial force in the pier according to BS EN 1998 - 2?
Approximately 0.1.
What stiffness is used in linear analysis for reinforced concrete piers?
The flexural stiffness of the uncracked gross section.
What does the longitudinal reinforcement ratio indicate?
It indicates the percentage of reinforcement used in structural elements to enhance their performance.
What is the least preferred solution for preventing unseating in new construction?
Restrainers.
What is the difference between Ground Type A and Ground Type C?
They refer to different soil conditions that affect seismic response and design considerations.
What height of piers should receive particular attention in earthquake resisting systems?
Piers shorter than 9 m or taller than 13 m.
What is the role of ground type in seismic design?
Ground type affects the seismic response and design requirements of structures.
What is the behavior factor for ductile design according to BS EN 1998-2?
The value is taken from Table 4.1 of BS EN 1998-2.
How is the natural vibration period of the pier calculated for ductile design?
Based on the tributary mass and cracked stiffness, initially assumed to be 30% of the flexural stiffness of the uncracked gross section.
How does the SDC strategy assist in bridge design?
It helps in selecting intended seismic behavior at the conceptual design stage.
What standards must be followed for reinforcement in piles?
BS EN 1992 - 1 - 1 and BS EN 1536.
What happens to shear capacity as plastic deformation develops in piers?
Shear capacity decreases.
How much can pile diameter be reduced when designed for ductile behavior?
By 5% to 29%.
How deep are the piles founded on bedrock?
30.5 m below ground level.
What is usually justifiable for tall piers in SDC B?
To design them for limited ductile behaviour.
What is the significance of the parameters ηk = 0.066 and ηk = 0.093?
They represent coefficients related to pier height and reinforcement behavior.
What is the significance of the transverse reinforcement ratio?
It indicates the amount of reinforcement needed for different structural behaviors.
What should be decided at the conceptual design stage regarding seismic behavior?
The type of intended seismic behavior.
What is the maximum allowable variation in stiffness between two piers within a frame according to Caltrans?
Not more than 50%.
What should be considered for bridges in SDC B?
Identification of an earthquake resisting system (ERS) for adequate seismic performance.
What is the friction angle of shearing resistance for Ground Type C?
35°.
What is the height of the pier discussed in the moment-curvature relationship?
9 m.
What is the behavior factor for limited ductile design?
1.5.
What is the concern regarding the seismic performance of piers?
Unintentional shear failure can occur under severe earthquakes.
How do isolation bearings contribute to bridge design?
They limit overall displacements during seismic events, with or without energy dissipaters.
What can cause the column to fail under design-level earthquake conditions?
Flexure, flexure-shear, and shear.
Why are shorter piers generally subjected to strong seismic motions?
Due to their short periods.
What is the first step in the structural design of a bridge pier after calculating seismic action effects?
Conducting the structural design in accordance with relevant clauses of BS EN 1998 - 2.
What initial estimate is often used for stiffness at the beginning of the design process?
30% of the flexural stiffness of the uncracked gross section.
What types of connections are mentioned in the context of seismic design?
Bearing connection and monolithic connection.
What is the preferred design behavior for critical importance bridges in poor site conditions?
Ductile behavior.
What are the three types of behavior classified in the context of transverse reinforcement?
Elastic, Limited-ductile, and Ductile.
What is the undrained shear strength of Ground Type B?
350 kN/m².
What is the normalized axial force (ηk) for the bridge piers?
0.093.
What is a key requirement for the earthquake resisting system (ERS) in SDC B?
It must provide a reliable load path for transmitting seismically induced forces.
What is the undrained shear strength of Ground Type D?
50 kN/m².
What are some methods to balance the stiffness and dynamic characteristics of a bridge?
Adjusting column height, using oversized drilled shafts, modifying end fixities, and adding seismic isolators.
What is the role of plastic hinges in bridge design?
They are placed at inspectable locations to allow for controlled deformation during seismic events.
What is the significance of articulation in bridge design?
It affects how forces are resisted within the structure, particularly during seismic events.
What is the allowable bearing pressure of the bedrock?
5000 kN/m².
What design behaviour should bridges classified as SDC A generally follow?
Elastic or limited ductile behaviour.
How does ductile design affect bridges in SDC A compared to SDC B?
The reduction effects are generally not as significant for bridges in SDC A.
What happens if piers of 5 m and 7 m heights cannot achieve elastic behavior?
The bridge must be designed for ductile or limited ductile behavior, or adopt seismic isolation.
What are the three types of behavior classified in the reinforcement ratio?
Elastic, Limited-ductile, and Ductile.
Why does limited ductile design lead to flexural-shear or shear failures?
Because BS EN 1998-2 does not require capacity design for bridges based on limited ductile behavior.
Why is balanced frame geometry important in bridge design?
It ensures similar seismic response during an earthquake and optimizes post-elastic seismic behavior.
What is the significance of confining reinforcement in bridge piers?
It is required in potential hinge regions when the normalized axial force exceeds 0.08.
What is usually justifiable for tall piers in seismic resisting systems?
Designing for limited ductile behavior.
What is the impact of ductile design on pile size and reinforcement for bridges in SDC B?
It can reduce the size and total amount of reinforcement.
What is the anticipated longitudinal reinforcement requirement for ductile behavior?
A minimum amount of longitudinal reinforcement is needed.
What does SDC stand for in seismic design?
Seismic Design Category.
What does the term 'Importance Class' refer to in the context of structural design?
It refers to the classification of structures based on their significance and the consequences of failure.
When might limited ductile behavior be chosen in bridge design?
When design conditions are more favorable for economic reasons.
What are the implications of designing for limited ductile behavior?
It allows for a reduction in design moments compared to elastic behavior.
What is the adhesion factor for the soil/pile interface in Ground Type B?
0.4.
What seismic conditions are the piers designed to resist?
Seismic inertial forces with seismic coefficients for Importance Class II and Ground Type C.
What is preferable for the design of critical bridges in Hong Kong?
To design the bridge for ductile behaviour.
What is the allowable lateral deflection of a pile?
Limited to 0.1 m.
What is the cross-section size of the bridge pier supported by the piled foundation?
3.0 m × 1.8 m.
What is the purpose of the fundamental mode method in seismic design for piers?
It is used for preliminary analysis to determine the horizontal design seismic action.
What is the total weight for seismic design of the pier?
15000 kN (14000 kN permanent weight + 1000 kN quasi-permanent weight).
What is the normalized displacement capacity factor (d̃p)?
The ratio of the plastic part of displacement capacity to the plastic part of ultimate displacement.
How are the seismic design situations for bridges in Hong Kong classified?
Primarily into two categories based on design spectral acceleration coefficients at a period of 1.0 sec.
What must be verified for ductile behavior in bridge piers?
The regions of plastic hinges must have adequate flexural strength to resist design moments.
How are sections designed for limited ductile or elastic behavior?
All sections are verified against design moments and shear forces derived from demand analysis.
How does the height of bridge piers affect their classification under SDC?
Piers shorter than 9 m or taller than 13 m may not be completely described by the SDC.
What is the normalized base seismic bending moment?
A measure used to evaluate the bending moment in relation to seismic loads.
What are the combinations of bridge importance class and ground type investigated in the seismic design?
Importance Class I with Ground Type B and C; Importance Class II with Ground Type C and D.
What is the role of the AASHTO Guide Specifications?
To provide guidelines for seismic design and analysis methods.
What type of soil is Ground Type C characterized by?
Medium dense residual soil with an undrained shear strength of 200 kN/m².
What is the normalized axial force mentioned for the pier in the study?
0.093.
What complicates the dynamic analysis of a bridge during an earthquake?
Skew and curvature, which couple lateral response in transverse and longitudinal directions.
What does SDC stand for in bridge design?
Seismic Design Categories.
What simplifying assumption is made regarding moments acting on the foundation?
They are assumed to be kept in equilibrium solely by the axial loads of the piles.
What special attention should be paid to in bridge design?
Bridges with piers shorter than 9 m or taller than 13 m.
What happens when abutments are flexibly connected to the deck?
It allows longitudinal movement, placing inertial forces on intermediate substructures.
In which soil conditions are the reduction effects more significant?
In cases of poor soil conditions.
What is a fusible shear key used for in bridge design?
To attain ductile response after the first yield of the keys during seismic events.
What is a potential risk when using multiple simple spans in bridge design?
The risk of unseating of spans and impact between adjacent spans during lateral deflection.
What is the implication of poor site conditions on bridge pier design?
The amount of longitudinal reinforcement may vary significantly with the design strategy adopted.
Why should the number of expansion joints in a bridge be minimized?
Bridges with continuous decks behave better under seismic conditions.
When might limited ductile behaviour be chosen in bridge design?
When design conditions are more favorable for economic reasons.
What criteria determine the pile diameter?
Axial compressive load, tensile uplift capacity, or allowable lateral deflection.
What is the expected design action effect on the foundation for limited ductile behavior?
It will result in the same design action effects as elastic behavior.
What reference peak ground acceleration is specified in SDMHR 2013 for seismic design?
0.12 g.
What is a risk for piers with aspect ratios not greater than 3.0?
Susceptibility to flexural-shear or shear failure during severe earthquakes.
What is the recommended design behaviour for bridges classified as SDC B?
Ductile behaviour.
What must be considered when using integral construction for superstructures?
The detail used to tie adjacent spans together and ensuring the superstructure can sustain induced forces.
What is the effect of adopting ductile design for a 7 m pier in SDC A?
The pile diameter is reduced by 13% and the volume of reinforcement is reduced by more than 40%.
What is the primary design consideration for bridge foundations under seismic actions?
They should remain elastic and not be used as sources of hysteretic energy dissipation.
What analysis is performed for each of the piers?
Pushover analysis.
What does the shear-displacement curve represent in the pushover analysis?
It can be represented by a bilinear approximation, accounting for shear capacity and plastic deformation.
How is the elastic seismic action derived for piers?
By multiplying the tributary mass by the relevant ordinate of the Type 2 elastic response spectrum.
What does SDC stand for in the context of bridge design?
Seismic Design Categories.
Why is lateral load path consideration important in bridge design?
It influences how the superstructure interacts with the substructure during lateral loading.
What is the minimum penetration requirement of the piles into rock?
0.3 m.
What is the center-to-center spacing of the bored piles?
3 times the pile diameter (d).
What can happen if a pier is over-reinforced?
The intended ductile behavior may not develop, leading to limited ductile or elastic behavior.
What is the design behavior for bridges classified as SDC A?
Essentially elastic behaviour.
What should bridges of SDC B be designed for?
Ductile behaviour.
What is the importance of evaluating the full-range behavior of piers?
To assess performance under intended ductile and limited ductile behavior.
What is the reduction in steel volume in piles when designed for ductile behavior?
By 4% to 41%.
In ductile design, what stiffness is used for equivalent linear analysis?
The secant stiffness at the theoretical yield point.
What is the design requirement for shear resistances in ductile bridge piers?
They should resist the 'capacity design effects' as determined by Clause 5.3 of BS EN 1998 - 2.
What detailing requirements must be followed for ductile and limited ductile concrete piers?
They must conform to the basic requirements set in Clauses 6.2 and 6.5 of BS EN 1998 - 2.
What is the requirement for transverse reinforcement in ductile piers?
More transverse reinforcement is required for heavier loaded piers intended for ductile behavior.
What is the effect of a continuous superstructure over piers?
It undertakes the bulk of transverse inertial forces, potentially preventing pier yielding.
How are elastic seismic actions modified in limited ductile and ductile design?
By dividing them by the relevant behavior factors.
What are the design moments at the base of the pier compared against?
The values normalized by those for the elastic design.
What is the role of the structural connection in the seismic design of piers?
It transmits the inertial force of the superstructure to the pier.
What is the effect of ductile design on the pile design for a 13 m pier in SDC B?
It is only slightly affected by the ductile design.
