I85PREP
⌘ K
CA Seismic study materials
CA Seismic study resources

CA Seismic practice questions

One question at a time. Build your CA Seismic understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Seismic Principles

Which statement best describes how a structure's fundamental period affects the seismic base shear computed by the equivalent lateral force procedure?

  1. Base shear is independent of period for all periods
  2. Base shear is largest for very flexible structures
  3. Base shear increases without limit as the period lengthens
  4. Base shear decreases as the period lengthens within the long-period region of the design spectrum Correct answer.

Explanation

In the long-period range the design spectral acceleration falls roughly in proportion to one over the period, so a longer fundamental period produces a smaller base shear coefficient. In the short-period plateau the base shear is essentially constant. This is why period estimation matters so much in the equivalent lateral force procedure.

Question 2Seismic Principles

A single-degree-of-freedom system has a natural period of 0.5 seconds. What is its natural frequency in hertz?

  1. 2.0 Hz Correct answer.
  2. 0.5 Hz
  3. 3.14 Hz
  4. 0.25 Hz

Explanation

Frequency is the reciprocal of period, so f equals one divided by T. With T equal to 0.5 seconds, the frequency is 1/0.5, which equals 2.0 hertz. The relationship holds for any linear single-degree-of-freedom oscillator.

Question 3Seismic Principles

Which structural characteristic most directly controls the ductility demand that a lateral-force-resisting system can tolerate during strong ground shaking?

  1. The building's total dead load
  2. The detailing of reinforcement and connections that permits inelastic deformation Correct answer.
  3. The number of stories above grade
  4. The plan dimension of the diaphragm

Explanation

Ductility capacity comes from detailing: confinement, splice location, joint reinforcement, and connection behavior that allow controlled yielding without brittle failure. Mass and geometry influence demand, but the ability to deform inelastically without losing strength is governed by detailing. This is why codes assign response modification factors tied to system type and detailing.

Question 4Seismic Principles

A building sits on a site with a softer soil profile than assumed in the original design. How does this generally change the design response spectrum compared with a stiff rock site?

  1. Spectral accelerations decrease across all periods
  2. The spectrum is unchanged because soil does not affect spectral shape
  3. Long-period spectral accelerations increase and the plateau shifts toward longer periods Correct answer.
  4. Short-period spectral accelerations increase while long-period values decrease

Explanation

Soft soils amplify long-period ground motion and shift the constant-acceleration plateau toward longer periods. Short-period amplification is generally greater on rock or stiff soil. Codes capture this through site coefficients that modify the spectrum at short and long periods.

Question 5Seismic Principles

A rigid concrete diaphragm is used in a building with a lateral-force-resisting system that is not symmetric in plan. What is the primary consequence of the diaphragm's rigidity?

  1. The building period becomes independent of the lateral system stiffness
  2. Base shear is reduced in proportion to the eccentricity
  3. Torsional response arises because the center of mass and center of rigidity do not coincide Correct answer.
  4. Torsional response is eliminated because the diaphragm cannot rotate

Explanation

A rigid diaphragm forces the floor to translate and rotate as a unit, so the offset between the center of mass and the center of rigidity produces torsional shears in the lateral elements. The eccentricity, not the rigidity alone, drives the torsion. Flexible diaphragms distribute load differently because they deform in plane.

Question 6Seismic Principles

Which quantity is defined as the ratio of the peak absolute acceleration of a structure to the peak ground acceleration during an earthquake?

  1. Ductility factor
  2. Acceleration amplification factor Correct answer.
  3. Overstrength factor
  4. Response modification factor

Explanation

The acceleration amplification factor compares the peak structural acceleration to the peak ground acceleration and reflects dynamic amplification. Ductility and response modification factors describe inelastic capacity and strength reduction, not dynamic amplification. Overstrength describes reserve capacity beyond design strength.

Question 7Seismic Principles

A structure is subjected to a ground motion with a dominant period close to its natural period. What phenomenon is expected?

  1. Immediate yielding without any amplification
  2. Resonance, producing large amplitude response Correct answer.
  3. Reduction of response to the static equivalent value
  4. Complete isolation of the structure from ground motion

Explanation

When the excitation period matches the natural period, the response amplifies strongly, a condition known as resonance. Spectral acceleration peaks near this period ratio. Real earthquakes have broadband content, but the dominant period still strongly influences response.

Question 8Seismic Principles

Which of the following best describes the purpose of a response spectrum in seismic design?

  1. To specify the required reinforcement in shear walls
  2. To compute the wind load on cladding
  3. To determine the soil bearing capacity at a site
  4. To give peak response of single-degree-of-freedom oscillators of varying period for a given ground motion Correct answer.

Explanation

A response spectrum plots the maximum response of single-degree-of-freedom oscillators with different periods and damping subjected to a specific ground motion. Design spectra smooth and envelope these results for code use. They are not a direct specification of member reinforcement or foundation capacity.

Question 9Seismic Principles

A building has a fundamental period of 1.0 second and a damping ratio of 5 percent. Using a design spectrum where the long-period branch is defined as S_a = 0.4/T times g, what is the design spectral acceleration at the fundamental period?

  1. 0.2 g
  2. 0.4 g Correct answer.
  3. 1.0 g
  4. 0.8 g

Explanation

Substituting T equal to 1.0 second into the long-period expression gives 0.4 divided by 1.0, which equals 0.4 g. The period value of one second makes the arithmetic direct. Damping of 5 percent is already the reference level for most design spectra.

Question 10Seismic Principles

A two-story building has equal floor weights of 100 kips each. A uniform lateral load distribution gives the first floor a force of 30 kips and the roof a force of 70 kips. What is the resulting base shear?

  1. 70 kips
  2. 30 kips
  3. 100 kips Correct answer.
  4. 140 kips

Explanation

Base shear equals the sum of all applied lateral story forces above the base. Adding 30 kips and 70 kips gives 100 kips. Equilibrium requires this total to be resisted at the foundation.

Question 11Seismic Principles

Which condition most commonly produces a soft-story mechanism in a multi-story building during an earthquake?

  1. A rigid foundation with no settlement
  2. A story with substantially lower lateral stiffness than the stories above it Correct answer.
  3. Extra dead load applied at the roof
  4. Uniform lateral stiffness at every story

Explanation

A soft story concentrates drift in the story with reduced stiffness, such as an open ground floor with few walls. The concentration of inelastic demand can produce a mechanism and collapse. Uniform stiffness distributes drift more evenly and is preferred.

Question 12Seismic Principles

Why does the equivalent lateral force procedure apply a vertical distribution exponent that shifts more force toward the top of a tall building?

  1. To model the effect of foundation flexibility
  2. To account for higher-mode contributions in the response of taller structures Correct answer.
  3. To reduce the total base shear
  4. To eliminate the need for a torsional analysis

Explanation

Taller structures respond with significant higher-mode content, so the actual force distribution is not purely triangular. The exponent raises the proportion of force applied near the roof to better approximate this behavior. The total base shear is unaffected by the distribution.

Question 13Seismic Principles

A cantilever shear wall has height h, thickness t, and length L. Which change most increases its flexural stiffness against lateral load?

  1. Halving the wall density
  2. Halving h
  3. Doubling t
  4. Doubling L Correct answer.

Explanation

Flexural stiffness of a cantilever varies with the cube of height and with the moment of inertia, which for a rectangular section varies with the cube of the dimension parallel to bending, here the wall length. Doubling the length increases stiffness by a factor of eight. Thickness affects stiffness only linearly.

Question 14Seismic Principles

Which factor of safety concept underlies the load combinations used in strength-level seismic design?

  1. Using service-level loads with no factors
  2. Applying a single global factor to all demands
  3. Ignoring dead load in seismic combinations
  4. Factoring loads and reducing nominal strengths to provide reliability margins Correct answer.

Explanation

Strength design applies load factors to demands and resistance factors to nominal capacities so that the probability of failure is acceptably low. Seismic combinations include dead plus seismic effects with specific factors. Service-level methods use unfactored loads and are used for different checks.

Question 15Seismic Principles

A building has a lateral system with a response modification factor R of 8. If the elastic base shear demand is 800 kips, what is the approximate design base shear under the simplified reduction?

  1. 400 kips
  2. 100 kips Correct answer.
  3. 800 kips
  4. 6400 kips

Explanation

Dividing the elastic demand by R gives 800 divided by 8, which equals 100 kips. The response modification factor accounts for ductility and overstrength that permit a reduced design strength. The structure then relies on inelastic behavior to resist the full elastic demand.

Question 16Seismic Principles

Which statement correctly describes the difference between a static equivalent approach and a modal response spectrum analysis?

  1. The static approach captures higher-mode effects more accurately
  2. Modal analysis requires no mass model
  3. Modal analysis combines modal maxima using statistical rules rather than simple superposition Correct answer.
  4. The static approach applies only to structures with no lateral system

Explanation

Modal response spectrum analysis computes peak modal responses and combines them with rules such as square-root-sum-of-squares because modal maxima do not occur simultaneously. The equivalent lateral force method uses a single mode shape approximation. Modal analysis generally captures higher-mode effects better, not worse.

Question 17Seismic Principles

During an earthquake, a building experiences a peak roof displacement of 4 inches and a peak ground displacement of 1 inch. What is the approximate displacement amplification factor?

  1. 1.0
  2. 2.0
  3. 5.0
  4. 4.0 Correct answer.

Explanation

The amplification factor is the ratio of peak structural displacement to peak ground displacement. Dividing 4 inches by 1 inch gives 4.0. This ratio reflects the dynamic amplification of the structure relative to the ground.

Question 18Seismic Principles

Why is accidental torsion included in seismic design even for nominally symmetric buildings?

  1. Because symmetric buildings never experience torsion
  2. Because torsion reduces base shear
  3. Because mass and stiffness distributions are never perfectly known and can be offset in practice Correct answer.
  4. Because accidental torsion replaces the need for diaphragm design

Explanation

Real buildings have uncertainties in mass, stiffness, and live load placement that can shift the center of mass or rigidity. Accidental eccentricity provisions account for this by applying a nominal offset. The result increases torsional demands on lateral elements.

Question 19Seismic Principles

Which type of foundation condition most increases the likelihood of site amplification of long-period ground motion?

  1. Shallow rock with high shear-wave velocity
  2. Deep soft soil deposits with low shear-wave velocity Correct answer.
  3. A rigid mat on dense gravel
  4. A basement embedded in stiff clay

Explanation

Deep soft soil deposits with low shear-wave velocity trap and amplify long-period waves, shifting the response spectrum toward longer periods. Rock and stiff soils tend to amplify short-period motion more. This is why site class matters in design spectra.

Question 20Seismic Principles

A structure's period lengthens as it yields during strong shaking. What effect does this generally have on the acceleration demand and displacement demand?

  1. Acceleration demand increases while displacement demand decreases
  2. Both demands remain unchanged
  3. Acceleration demand decreases while displacement demand increases Correct answer.
  4. Both acceleration and displacement demand decrease

Explanation

Period elongation moves the structure down the descending branch of the spectrum, reducing spectral acceleration and hence force demand. However, the same long-period response typically produces larger displacements. This trade-off is central to ductile design.

Question 21Seismic Principles

Which statement best explains why diaphragms must be designed for both inertial forces and transfer forces?

  1. Diaphragms only resist gravity loads
  2. Diaphragms collect inertial forces from their own mass and distribute lateral forces to vertical elements, including forces from horizontal offsets Correct answer.
  3. Diaphragms are never part of the lateral-force-resisting system
  4. Diaphragms resist only wind loads

Explanation

A diaphragm acts as a horizontal beam that gathers inertial forces from its mass and delivers them to the vertical lateral system. Where lateral elements are offset or discontinuous, the diaphragm must also transfer forces between them. Both roles produce in-plane shear and bending demands.

Question 22Seismic Principles

A building's lateral system consists of two shear walls of equal stiffness connected by a flexible diaphragm. Where is the center of rigidity located relative to the walls?

  1. At the location of the stiffer wall
  2. At the geometric centroid of the two walls Correct answer.
  3. Outside the building footprint
  4. At the center of mass regardless of wall stiffness

Explanation

The center of rigidity is the stiffness-weighted centroid of the lateral-force-resisting elements. For two equal-stiffness walls, it lies midway between them. Unequal stiffness would shift it toward the stiffer element.

Question 23Seismic Principles

A 10-story building has a period of 1.0 second and is subjected to a ground motion with a dominant period of 0.3 seconds. Which response characteristic is most likely?

  1. Strong resonant amplification because periods are close
  2. Immediate collapse due to period matching
  3. Relatively low amplification because the periods are well separated Correct answer.
  4. Base shear equal to the peak ground acceleration times the weight

Explanation

Amplification is greatest when the structure period is near the dominant ground motion period. With a 1.0-second structure and a 0.3-second excitation, the ratio is far from unity, so resonant amplification is limited. The response spectrum confirms lower spectral acceleration at the longer period.

Question 24Seismic Principles

A building has an extreme torsional irregularity. How does the code generally treat the design forces for the lateral-force-resisting elements on the flexible side?

  1. They are based only on the accidental eccentricity
  2. They must be increased to account for the additional torsional demand Correct answer.
  3. They may be reduced because the flexible side attracts less force
  4. They are unaffected because torsion is handled by the diaphragm

Explanation

Torsional irregularity provisions amplify the design forces in the lateral elements to account for the increased torsional response and the larger displacement of the flexible side. The amplification is applied in addition to the nominal torsional moment. Ignoring it would underestimate demands on elements that experience the largest drift.

Question 25Seismic Principles

A structure has a natural period of 0.4 seconds and a damping ratio of 2 percent instead of the reference 5 percent. What is the general effect on its spectral acceleration demand?

  1. Demand decreases because lower damping softens the structure
  2. Demand is unchanged because damping does not affect spectra
  3. Demand decreases because damping is inversely related to period
  4. Demand increases because lower damping produces less energy dissipation Correct answer.

Explanation

Lower damping reduces energy dissipation per cycle, so response amplitudes and spectral accelerations increase near resonance. Design spectra are typically referenced to 5 percent damping and adjusted for other values. The adjustment amplifies demand when damping is below the reference.

Question 26Seismic Principles

Which soil profile type generally amplifies ground shaking the most during an earthquake?

  1. Soft clay with a low shear-wave velocity Correct answer.
  2. Competent bedrock at the surface
  3. Weathered rock at shallow depth
  4. Dense gravel with a high shear-wave velocity

Explanation

Soft soils have low shear-wave velocity, which traps and amplifies seismic waves relative to stiff rock. The impedance contrast between soft soil and underlying rock increases the amplitude of shaking at the surface.

Question 27Seismic Principles

Which structural property is most directly measured by the fundamental period of a building?

  1. Its foundation bearing pressure
  2. Its ductility under cyclic loading
  3. Its ultimate moment capacity
  4. Its overall lateral stiffness relative to its mass Correct answer.

Explanation

The fundamental period depends on both mass and lateral stiffness, with stiffer or lighter buildings having shorter periods. It therefore reflects how the structure will respond dynamically to ground motion.

Question 28Seismic Principles

In seismic design, what does the term base shear refer to?

  1. The shear carried by a single interior column
  2. The total lateral design force applied at the base of the structure Correct answer.
  3. The overturning moment at the foundation
  4. The vertical reaction at the footing due to dead load

Explanation

Base shear is the total horizontal force the lateral-force-resisting system must resist, derived from the building's seismic weight. It represents the overall inertial demand distributed over the height.

Question 29Seismic Principles

Which framing system is typically assigned a lower response modification factor R than a special moment frame?

  1. A special concentrically braced frame
  2. A dual system with special frames
  3. An ordinary moment frame Correct answer.
  4. A special shear wall

Explanation

Ordinary moment frames have limited detailing and ductility, so codes assign them a lower R than special systems. A lower R reflects less energy dissipation capacity and results in higher design forces.

Question 30Seismic Principles

What is the primary purpose of a shear wall in a building's lateral-force-resisting system?

  1. To reduce the building's seismic weight
  2. To carry only vertical gravity loads from the floors
  3. To resist horizontal forces through in-plane stiffness and strength Correct answer.
  4. To provide architectural separation between spaces

Explanation

Shear walls act as stiff vertical elements that resist lateral loads in their own plane. Their high in-plane stiffness limits drift and distributes seismic forces to the foundation.

Question 31Seismic Principles

Which phenomenon describes the amplification of ground motion that occurs when soft soil overlies stiff rock?

  1. Base isolation
  2. Soil liquefaction
  3. Ductile yielding
  4. Site amplification Correct answer.

Explanation

Site amplification occurs because soft soil layers trap seismic energy and increase surface shaking relative to rock. The impedance contrast and low damping of the soil layer drive this effect.

Question 32Seismic Principles

Which quantity describes the maximum displacement of a structure relative to its base during an earthquake?

  1. Base shear
  2. Drift Correct answer.
  3. Natural period
  4. Overturning moment

Explanation

Drift is the relative lateral displacement between two levels of a structure, often expressed as a story drift ratio. It is a key measure of seismic performance because excessive drift damages nonstructural elements.

Question 33Seismic Principles

What does the seismic weight W used in the equivalent lateral force procedure primarily include?

  1. Only the weight of the lateral-force-resisting system
  2. The total dead load plus applicable portions of other loads Correct answer.
  3. The wind load applied to the building
  4. Only the live load on the roof

Explanation

Seismic weight is dominated by the total dead load, with specified fractions of storage and other loads added where appropriate. This mass generates the inertial forces during an earthquake.

Question 34Seismic Principles

A rigid diaphragm distributes lateral forces among vertical elements in proportion to which property?

  1. Their tributary floor area
  2. Their material density
  3. Their relative lateral stiffness Correct answer.
  4. Their individual column heights

Explanation

A rigid diaphragm ties the vertical elements together so they deflect together, distributing force according to stiffness. Stiffer elements attract a larger share of the lateral load.

Question 35Seismic Principles

A structure has a natural period of 0.5 seconds and a damping ratio of 10 percent instead of 5 percent. What is the general effect on peak response near resonance?

  1. The peak response is unchanged
  2. The peak response increases
  3. The peak response decreases Correct answer.
  4. The natural period doubles

Explanation

Higher damping dissipates more energy per cycle, reducing the resonant amplification of response. Near resonance, the peak displacement and acceleration amplitudes both decrease as damping increases.

Question 36Seismic Principles

A building has a seismic base shear of 400 kips and a seismic weight of 2000 kips. What is the approximate base shear coefficient?

  1. 5.0
  2. 0.50
  3. 0.05
  4. 0.20 Correct answer.

Explanation

The base shear coefficient is the base shear divided by the seismic weight, giving 400 divided by 2000. This equals 0.20, representing the lateral force as a fraction of building weight.

Question 37Seismic Principles

Why are special moment frames detailed with closely spaced transverse reinforcement in beam-column joints?

  1. To reduce the natural period of the structure
  2. To increase the building's seismic weight
  3. To confine concrete and develop ductile hinging during strong shaking Correct answer.
  4. To prevent all inelastic deformation in the frame

Explanation

Close transverse reinforcement confines the concrete and improves ductility so the frame can undergo large inelastic deformations without brittle failure. This detailing allows the frame to dissipate seismic energy.

Question 38Seismic Principles

Which condition is most likely to cause a discontinuity in a building's lateral-force-resisting system?

  1. Uniform stiffness along the building height
  2. Matching stiffness on opposite building faces
  3. A continuous column line from roof to foundation
  4. A shear wall that stops at an upper floor Correct answer.

Explanation

A vertical element that terminates above the base creates a discontinuity that concentrates forces and can cause a soft story or excessive drift. Continuous load paths are preferred to avoid abrupt stiffness changes.

Question 39Seismic Principles

A structure's natural period is lengthened by adding flexible base isolation. What is the primary benefit during an earthquake?

  1. The structure's foundation uplift is increased
  2. The structure's seismic weight is reduced
  3. The structure's acceleration demand is reduced Correct answer.
  4. The structure's damping is eliminated

Explanation

Base isolation shifts the structure's period to a range where ground motion acceleration is lower, reducing the forces transmitted to the superstructure. The isolation layer also adds damping to limit displacement.

Question 40Seismic Principles

What is the main reason codes limit story drift in seismic design?

  1. To increase the natural period of the structure
  2. To control damage to nonstructural elements and prevent instability Correct answer.
  3. To reduce the building's dead load
  4. To eliminate the need for a lateral-force-resisting system

Explanation

Excessive story drift damages cladding, partitions, and other nonstructural elements and can lead to instability. Drift limits protect both life safety and the building's function after an earthquake.

Question 41Seismic Principles

Which statement best describes the role of redundancy in a seismic-force-resisting system?

  1. Redundancy increases the building's seismic weight
  2. A single stiff element is relied upon for all lateral resistance
  3. Redundancy eliminates the need for ductile detailing
  4. Multiple load paths reduce the consequence of a single element's failure Correct answer.

Explanation

Redundancy provides alternate load paths so that failure or yielding of one element does not cause collapse. Codes recognize this by permitting a reduced design force where redundancy is present.

Question 42Seismic Principles

A building has a period of 0.2 seconds and a ground motion with a dominant period of 1.0 second. What is the expected response?

  1. The structure responds relatively stiffly with low dynamic amplification Correct answer.
  2. The structure experiences maximum drift at the roof
  3. The structure resonates strongly with the ground motion
  4. The structure's base shear vanishes

Explanation

Because the structure's period is much shorter than the dominant ground period, it behaves in a stiff, acceleration-controlled range with limited amplification. Resonance requires the periods to be close.

Question 43Seismic Principles

In the equivalent lateral force procedure, what does the vertical distribution exponent k depend on?

  1. The fundamental period of the structure Correct answer.
  2. The soil profile at the site
  3. The damping ratio of the structure
  4. The building's occupancy category

Explanation

The exponent k varies with the fundamental period, shifting the distribution of lateral force over the height. Longer-period structures receive a distribution more concentrated toward upper levels.

Question 44Seismic Principles

What is the purpose of an importance factor in seismic design?

  1. To account for the ductility of the lateral system
  2. To adjust the building's natural period
  3. To reduce the seismic weight of essential facilities
  4. To increase design forces for structures whose failure would be especially costly Correct answer.

Explanation

The importance factor raises design forces for essential or hazardous facilities so they have a lower probability of failure. It reflects the consequences of failure rather than the structure's dynamic properties.

Question 45Seismic Principles

A building with a flexible diaphragm and two lateral-force-resisting walls is analyzed. Why must the diaphragm be designed for its own inertial force?

  1. The diaphragm reduces the building's seismic weight
  2. The diaphragm carries only vertical loads from the roof
  3. The diaphragm's mass generates horizontal forces that must be transferred to the walls Correct answer.
  4. The diaphragm isolates the walls from ground motion

Explanation

The diaphragm has mass, so during shaking it develops inertial forces that must be collected and delivered to the vertical lateral system. Designing only for the wall reactions would omit this distributed demand.

Question 46Seismic Principles

Which design approach explicitly accounts for the inelastic energy dissipation of a structure during a major earthquake?

  1. Using a response modification factor greater than one Correct answer.
  2. Ignoring ductility in the lateral system
  3. Using a static analysis with no force reduction
  4. Designing for elastic forces from the maximum credible earthquake

Explanation

A response modification factor greater than one reduces elastic design forces to account for the structure's ductility and energy dissipation. This permits economical design while relying on controlled inelastic behavior.

Question 47Seismic Principles

Two buildings have equal mass, but one has a lateral stiffness four times that of the other. What is the ratio of their natural periods?

  1. The periods are equal
  2. The stiffer building has twice the period
  3. The stiffer building has one quarter the period
  4. The stiffer building has half the period Correct answer.

Explanation

Period is proportional to the square root of mass divided by stiffness, so quadrupling stiffness halves the period. The stiffer building therefore has half the natural period of the other.

Question 48Seismic Principles

A building has a torsional irregularity because its center of mass is offset from its center of rigidity. What is the most appropriate design response?

  1. Remove all lateral elements on the flexible side
  2. Reduce the seismic weight to eliminate torsion
  3. Increase the design forces on elements that resist torsion Correct answer.
  4. Assume the diaphragm is perfectly rigid and ignore the offset

Explanation

When mass and rigidity centers do not coincide, the building twists and the perimeter elements carry additional shear. Codes require amplifying torsional effects on the elements resisting that torsion.

Question 49Seismic Principles

Which statement best explains why soft-story mechanisms are especially dangerous in seismic design?

  1. The soft story increases the building's damping
  2. Inelastic deformation concentrates in one story, leading to collapse Correct answer.
  3. The building's seismic weight is reduced at the soft story
  4. The soft story shortens the building's natural period

Explanation

A soft story is much less stiff than the stories above, so drift and inelastic demand concentrate there. This concentration can exhaust the story's deformation capacity and trigger collapse.

Question 50Seismic Principles

A structure has a natural period of 1.5 seconds and is subjected to a ground motion with a dominant period of 0.3 seconds. What is the expected dynamic behavior?

  1. The structure's base shear reaches its maximum value
  2. The structure resonates strongly with the ground motion
  3. The structure behaves as a rigid body with the ground
  4. The structure responds with reduced acceleration and larger displacement Correct answer.

Explanation

A long-period structure is much more flexible than the short-period ground motion, so it tends to remain relatively still while its base moves, reducing acceleration but increasing relative displacement. This is the displacement-controlled range of the spectrum.