What does the longitudinal reinforcement ratio indicate?
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It indicates the percentage of reinforcement used in structural elements to enhance their performance.
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What does the longitudinal reinforcement ratio indicate?
It indicates the percentage of reinforcement used in structural elements to enhance their performance.
What aspect ratio indicates susceptibility to flexural-shear failure in piers?
Aspect ratios not exceeding 3.0.
What is the effect of designing a pier for ductile behavior compared to elastic behavior?
The design moment can generally be reduced significantly.
What does SDC stand for in seismic design?
Seismic Design Category.
What are the three types of behavior classified in the reinforcement ratio?
Elastic, Limited-ductile, and Ductile.
At what aspect ratio is a pier prone to shear failure under limited ductile behavior?
An aspect ratio as small as 1.7.
What is the purpose of the Seismic Design Category (SDC)?
To determine different requirements for analysis methods and column design details.
What types of connections are mentioned in the context of seismic design?
Bearing connection and monolithic connection.
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 design strategy does ductile design employ to avoid brittle shear failures?
Capacity design strategy.
What is the least preferred solution for preventing unseating in new construction?
Restrainers.
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.
What is the significance of Importance Class I and Ground Type A in seismic design?
They indicate specific design criteria for seismic performance.
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.
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.
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.
What is the preferred design behavior for critical importance bridges in poor site conditions?
Ductile behavior.
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 significance of the transverse reinforcement ratio?
It indicates the amount of reinforcement needed for different structural behaviors.
What is the normalized base seismic bending moment?
A measure used to evaluate the bending moment in relation to seismic loads.
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.
How does the intended behavior of a bridge affect foundation design?
It affects the magnitude of seismic actions transmitted to the foundation.
When is it preferable to design a bridge for ductile behavior?
In cases of moderate-to-high seismicity.
When might limited ductile behavior be chosen in bridge design?
When design conditions are more favorable for economic reasons.
Why is balanced frame geometry important in bridge design?
It ensures similar seismic response during an earthquake and optimizes post-elastic seismic behavior.
How does pier height affect seismic design moments?
Different pier heights can influence the design moments required for seismic resistance.
What are the three types of behavior classified in the context of transverse reinforcement?
Elastic, Limited-ductile, and Ductile.
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.
What should be decided at the conceptual design stage regarding seismic behavior?
The type of intended seismic behavior.
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 height of piers should receive particular attention in earthquake resisting systems?
Piers shorter than 9 m or taller than 13 m.
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 is the importance of the pier height in seismic design?
It influences the design requirements and reinforcement ratios.
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 significance of confining reinforcement in bridge piers?
It is required in potential hinge regions when the normalized axial force exceeds 0.08.
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 undrained shear strength of Ground Type B?
350 kN/m².
Why are shorter piers generally subjected to strong seismic motions?
Due to their short periods.
What is the maximum allowable variation in stiffness between two piers within a frame according to Caltrans?
Not more than 50%.
What is the role of the AASHTO Guide Specifications?
To provide guidelines for seismic design and analysis methods.
What is the role of ground type in seismic design?
Ground type affects the seismic response and design requirements of structures.
What are the two categories of normalized axial forces studied for bridge piers?
0.066 and 0.093.
What is generally not required for bridges in SDC A due to low seismic hazard levels?
Seismic analysis.
What is the adhesion factor for the soil/pile interface in Ground Type B?
0.4.
What is usually justifiable for tall piers in seismic resisting systems?
Designing for limited ductile behavior.
What is the recommended maximum skew angle for bridge design?
Less than 30 degrees if possible.
What is the normalized axial force (ηk) for the bridge piers?
0.093.
What happens to the tributary mass of the deck when the articulation changes to integral?
The tributary mass is halved.
What should be considered for bridges in SDC B?
Identification of an earthquake resisting system (ERS) for adequate seismic performance.
What type of soil is Ground Type C characterized by?
Medium dense residual soil with an undrained shear strength of 200 kN/m².
Why is designing for elastic behavior often considered wasteful?
Because it should not be accepted in most cases.
What is the preferred strategy to achieve a continuous deck in bridge design?
Using continuous or integral construction.
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 the range of clear height for the bridge piers studied?
From 5 m to 17 m.
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 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 is the friction angle of shearing resistance for Ground Type C?
35°.
What is the normalized axial force mentioned for the pier in the study?
0.093.
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.
Why should the number of expansion joints in a bridge be minimized?
Bridges with continuous decks behave better under seismic conditions.
What is preferable for the design of critical bridges in Hong Kong?
To design the bridge for ductile behaviour.
What should be conducted for bridges in SDC B?
Seismic analysis and a displacement demand to capacity check.
What is the undrained shear strength of Ground Type D?
50 kN/m².
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 height of the pier discussed in the moment-curvature relationship?
9 m.
What complicates the dynamic analysis of a bridge during an earthquake?
Skew and curvature, which couple lateral response in transverse and longitudinal directions.
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.
When might limited ductile behaviour be chosen in bridge design?
When design conditions are more favorable for economic reasons.
What may apply to bridges in SDC C and above?
More stringent detailing rules.
What is the allowable lateral deflection of a pile?
Limited to 0.1 m.
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 type of connection does the pier have to the deck?
Monolithic connection.
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 behavior factor for limited ductile design?
1.5.
What does SDC stand for in bridge design?
Seismic Design Categories.
How does the SDC strategy assist in bridge design?
It helps in selecting intended seismic behavior at the conceptual design stage.
What criteria determine the pile diameter?
Axial compressive load, tensile uplift capacity, or allowable lateral deflection.
What must be verified for the piles in bridge foundations?
They must have sufficient axial and lateral resistances.
What is the cross-section size of the bridge pier supported by the piled foundation?
3.0 m × 1.8 m.
What analysis is performed for each of the piers?
Pushover analysis.
What is the design behavior for bridges classified as SDC A?
Essentially elastic behaviour.
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 concern regarding the seismic performance of piers?
Unintentional shear failure can occur under severe earthquakes.
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 standards must be followed for reinforcement in piles?
BS EN 1992 - 1 - 1 and BS EN 1536.
What is the height of the bridge pier?
9 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 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.
What should bridges of SDC B be designed for?
Ductile behaviour.
How do isolation bearings contribute to bridge design?
They limit overall displacements during seismic events, with or without energy dissipaters.
What happens to shear capacity as plastic deformation develops in piers?
Shear capacity decreases.
What is the maximum clear distance between longitudinal bars in a pile?
Should not exceed 200 mm.
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 is the total weight for seismic design of the pier?
15000 kN (14000 kN permanent weight + 1000 kN quasi-permanent weight).
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 can cause the column to fail under design-level earthquake conditions?
Flexure, flexure-shear, and shear.
What special attention should be paid to in bridge design?
Bridges with piers shorter than 9 m or taller than 13 m.
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 importance of evaluating the full-range behavior of piers?
To assess performance under intended ductile and limited ductile behavior.
How much can pile diameter be reduced when designed for ductile behavior?
By 5% to 29%.
What is the normalized axial force in the pier according to BS EN 1998 - 2?
Approximately 0.1.
What reference peak ground acceleration is specified in SDMHR 2013 for seismic design?
0.12 g.
What is the normalized displacement capacity factor (d̃p)?
The ratio of the plastic part of displacement capacity to the plastic part of ultimate displacement.
What does SDC stand for in the context of bridge design?
Seismic Design Categories.
Why are shorter piers generally subjected to strong seismic motions?
Due to their short periods.
What happens when abutments are flexibly connected to the deck?
It allows longitudinal movement, placing inertial forces on intermediate substructures.
What is the reduction in steel volume in piles when designed for ductile behavior?
By 4% to 41%.
How deep are the piles founded on bedrock?
30.5 m below ground level.
What stiffness is used in linear analysis for reinforced concrete piers?
The flexural stiffness of the uncracked gross section.
What is a risk for piers with aspect ratios not greater than 3.0?
Susceptibility to flexural-shear or shear failure during severe earthquakes.
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.
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 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.
In which soil conditions are the reduction effects more significant?
In cases of poor soil conditions.
What is the allowable bearing pressure of the bedrock?
5000 kN/m².
In ductile design, what stiffness is used for equivalent linear analysis?
The secant stiffness at the theoretical yield point.
What is usually justifiable for tall piers in SDC B?
To design them for limited ductile behaviour.
What is the effect of a continuous superstructure over piers?
It undertakes the bulk of transverse inertial forces, potentially preventing pier yielding.
What is the recommended design behaviour for bridges classified as SDC B?
Ductile behaviour.
What must be verified for ductile behavior in bridge piers?
The regions of plastic hinges must have adequate flexural strength to resist design moments.
What is the minimum penetration requirement of the piles into rock?
0.3 m.
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 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 design behaviour should bridges classified as SDC A generally follow?
Elastic or limited ductile behaviour.
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 is the thickness of the pile cap?
2 m.
How are elastic seismic actions modified in limited ductile and ductile design?
By dividing them by the relevant behavior factors.
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 impact of ductile design on pile size and reinforcement for bridges in SDC B?
It can reduce the size and total amount of reinforcement.
How are sections designed for limited ductile or elastic behavior?
All sections are verified against design moments and shear forces derived from demand analysis.
What is the center-to-center spacing of the bored piles?
3 times the pile diameter (d).
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 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.
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 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 type of soil cover is above the pile cap?
1.5 m.
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 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 anticipated longitudinal reinforcement requirement for ductile behavior?
A minimum amount of longitudinal reinforcement is needed.
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 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 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.
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.
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 is the requirement for transverse reinforcement in ductile piers?
More transverse reinforcement is required for heavier loaded piers intended for ductile behavior.
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.
