Wind, Seismic, Robustness, and Progressive Collapse Design

Introduction and context

Steel buildings are efficient because steel has high strength-to-weight ratio, predictable material properties, and the ability to form ductile structural systems. These advantages do not, by themselves, guarantee safety under wind, earthquakes, accidental actions, or local damage. Lateral forces may reverse repeatedly, connections may control the response, diaphragms must transfer forces between floors and vertical resisting elements, and a local failure can become disproportionate if alternative load paths are inadequate.

This chapter develops an integrated approach to lateral and abnormal-event design. The central idea is that safety depends on the behaviour of the complete structural system rather than on isolated member strength. Members, connections, bracing, diaphragms, foundations, cladding interfaces, and nonstructural components must work together. Design must therefore address strength, stiffness, ductility, stability, robustness, redundancy, constructability, inspection, and the consequences of failure.

The numerical provisions used in practice must be taken from the governing national standard. Typical references include ASCE 7 and AISC 360/AISC 341 in the United States, Eurocodes EN 1991, EN 1998 and EN 1993 in Europe, and corresponding national standards elsewhere. The principles in this chapter are transferable, but numerical coefficients and prescribed load combinations are jurisdiction-specific.

Learning objectives

By the end of this chapter, the reader should be able to:

1. Explain how wind and seismic actions are transmitted through a steel building.
2. Distinguish strength, stiffness, ductility, energy dissipation, redundancy, and robustness.
3. Select and compare moment frames, braced frames, diaphragms, and dual systems.
4. Apply basic wind, seismic, drift, capacity-design, and tying concepts.
5. Recognize connection and detailing requirements for cyclic and accidental loading.
6. Evaluate a progressive-collapse scenario using alternate load paths and suitable analysis levels.
7. Identify limitations, uncertainties, ethical responsibilities, and quality-control requirements.

1. The structural load path under lateral action

A lateral load path is the sequence through which an action travels from its point of application to the ground. For wind, pressure acts on cladding and is transferred through fasteners, girts, floor and roof diaphragms, collectors, braces or rigid frames, columns, and foundations. For earthquakes, inertial forces originate in the mass of floors, roofs, partitions, equipment, and cladding. They pass through diaphragms and collectors to the seismic-force-resisting system and then into the ground.

A complete load path should be:

• continuous in both principal horizontal directions;
• sufficiently strong at members, connections, collectors, diaphragms, and foundations;
• stiff enough to control drift and nonstructural damage;
• ductile where inelastic response is intended;
• stable under load reversal and second-order effects; and
• inspectable and constructible.

The diaphragm is not merely a horizontal plate. It distributes lateral forces among vertical elements, transfers forces around openings, and may act as a collector or chord. Openings, discontinuous framing, weak connections, and flexible roof systems can substantially change the assumed distribution.

A useful conceptual distinction is between force-resisting elements and force-transferring elements. Braces, beams, columns, and moment connections resist major actions, while deck fasteners, collectors, drag struts, panel joints, and anchorage transmit those actions. Failure of a transferring element can interrupt the entire load path even when the principal members have ample capacity.

2. Wind design of steel buildings

2.1 Wind action and pressure

Wind design begins with the wind climate, building exposure, height, geometry, terrain, topography, importance, and internal pressure condition. Codes commonly provide a velocity-pressure relationship of the general form

where q_z is velocity pressure at height z, in N/m²; ρ is air density, in kg/m³; and V_z is design wind speed at height z, in m/s. The expression follows from fluid mechanics, while the design code modifies it through exposure, gust, directionality, importance, and other factors.

A simplified net pressure on a building surface may be represented as

where p is net design pressure; G is a gust-effect factor; C_p is an external pressure coefficient; q_i is an internal reference velocity pressure; and C_pi is an internal pressure coefficient. The signs and coefficients must be selected from the applicable standard. This equation is not a substitute for code-specific pressure procedures.

For a surface area A, the resultant force is approximately

provided the pressure can reasonably be treated as uniform over that area. For overall building design, pressures are integrated over tributary areas and converted into story shears, overturning moments, diaphragm forces, and local component reactions.

2.2 Serviceability and strength

Wind design has at least two distinct objectives. Strength design prevents member, connection, anchorage, and foundation failure. Serviceability design limits lateral drift, acceleration, vibration, cladding movement, water penetration, and occupant discomfort. A building may satisfy ultimate strength requirements while still suffering unacceptable façade damage or excessive perceptible motion.

The elastic interstory drift ratio is commonly defined as

where Δ is relative lateral displacement between two adjacent floors and h is the corresponding story height. The ratio is dimensionless. Its allowable value depends on the code, occupancy, structural system, and whether the check concerns strength-level, service-level, or amplified design displacement.

Second-order effects become important when axial compression acts through a displaced geometry. A basic stability parameter is

where P is the vertical gravity load above the story, Δ is story displacement, V is story shear, and h is story height. This expression is a dimensionless measure of additional overturning effect relative to first-order story shear moment. Codes provide the applicable limits and amplification procedures; the simplified indicator is not a universal acceptance criterion.

2.3 Wind-induced dynamic response

Tall, slender, lightly damped, or flexible buildings may respond dynamically to turbulence, vortex shedding, and cross-wind excitation. The natural period, mode shapes, damping, mass distribution, and aerodynamic form influence response. Wind-tunnel testing or computational fluid dynamics may be appropriate when code procedures do not adequately represent unusual geometry or sensitivity.

Designers should check both along-wind and cross-wind response, local cladding pressures, fatigue-sensitive details, roof uplift, construction-stage stability, and temporary conditions. Wind bracing that is effective in the completed building may be incomplete during erection.

3. Seismic design principles

3.1 Inertial action and dynamic behaviour

Earthquake forces arise because building mass resists acceleration. A simplified equivalent-static relationship is

where V is design base shear, C_s is the code-defined seismic response coefficient, and W is effective seismic weight. The coefficient depends on hazard, site class, structural period, ductility or response modification, importance, and code limits. The equation is applicable only when the building qualifies for the code’s equivalent-static procedure.

The approximate fundamental period of a building is often estimated using a code expression such as

where T_a is approximate period, h_n is building height, and C_t and x are code-specific constants. The approximate period is used for preliminary analysis or within specified code limits; it is not a universal dynamic law.

A linear elastic idealization is useful for predicting forces and displacements, but severe earthquakes may cause yielding. The design objective is usually controlled inelastic behaviour: selected components yield and dissipate energy while critical connections, columns, diaphragms, foundations, and stability elements remain sufficiently reliable.

3.2 Seismic-force-resisting systems

Common steel systems include:

System selection should consider height, regularity, drift, architectural requirements, soil conditions, erection sequence, inspection capability, and the consequences of damage. A nominally strong system may perform poorly if its deformation mechanism is brittle or if force transfer between subsystems is not demonstrated.

3.3 Ductility and capacity design

Ductility is the ability to undergo significant inelastic deformation while retaining resistance. It is not simply the ratio of ultimate displacement to first yield, because useful ductility also requires stable hysteresis, adequate low-cycle fatigue resistance, and protection against local and global buckling.

Capacity design establishes a hierarchy: designated ductile zones are permitted to yield, while non-yielding components are proportioned for the probable strength of those zones plus relevant dynamic and overstrength effects. For a brace connection, for example, the connection may need to resist the probable tensile yield or tensile rupture-related force of the brace, as well as compression-related effects and force reversal. Designing only for the elastic analysis force can produce a connection that fails before the intended ductile member mechanism develops.

For a plastic hinge, the idealized plastic moment is often written as

where M_p is plastic moment, F_y is yield stress, and Z_p is plastic section modulus. This relationship assumes a compact, adequately braced section with suitable material behaviour and a bending mechanism governed by yielding rather than local buckling. It does not by itself establish a qualified seismic hinge.

Brace buckling deserves special attention. A slender compression brace can lose resistance after buckling, while its connections must withstand tensile yielding, compression instability, gusset-plate deformation, and cyclic reversal. Gusset plates require appropriate clearance and out-of-plane restraint so that the intended brace mechanism is not blocked.

3.4 Diaphragms, collectors, and torsion

Floor and roof diaphragms transfer inertial forces to vertical resisting elements. Their design includes in-plane shear, chord forces, collector or drag forces, attachment to beams, forces around openings, and compatibility with vertical-frame deformation. Composite slabs may provide substantial diaphragm stiffness, but the steel deck, slab reinforcement, shear connectors, welds, screws, and edge details must be considered as a system.

Irregular mass or stiffness distribution causes torsion. Accidental torsion allowances in codes represent uncertainty in mass, stiffness, and ground motion. Designers should not rely on a single idealized centre-of-mass model when diaphragm flexibility, discontinuity, or large openings produce significant three-dimensional effects.

4. Connections and detailing for cyclic and lateral actions

Connections are often the governing part of a steel lateral system. A complete connection design considers shear, axial force, bending, prying, bolt slip or bearing, weld strength, block shear, net-section fracture, local yielding, panel-zone behaviour, gusset stability, fatigue, corrosion, erection tolerances, and force reversal.

For cyclic seismic response, details must avoid brittle fracture and severe stress concentration. Relevant practices include:

• use of qualified weld procedures and suitable weld access holes;
• control of material toughness where fracture risk is significant;
• avoidance of abrupt geometry changes;
• adequate bolt installation and inspection;
• continuity plates, doubler plates, and panel-zone checks where required;
• protected zones around intended plastic hinges; and
• verification that protected components do not receive unanticipated attachments or penetrations.

A connection’s nominal strength is not equivalent to its cyclic performance. Fracture toughness, low-cycle fatigue, local buckling, residual stress, weld quality, and deformation compatibility may control. Inspection and documentation are therefore part of structural design, not merely construction administration.

5. Robustness and progressive collapse

5.1 Concepts and distinctions

Robustness is the ability of a structure to tolerate unforeseen or localized events without disproportionate damage. Redundancy is the presence of multiple load paths or alternate resisting components. Resilience is broader and includes preparation, response, recovery, and adaptation. A redundant structure is not automatically robust: if all alternate paths depend on one weak connection or a brittle diaphragm, local damage can still spread.

Progressive collapse is a chain reaction in which local failure causes redistribution and subsequent failure of additional components. It may result from impact, explosion, fire, construction error, severe corrosion, abnormal overload, or other accidental actions. Because the initiating event is uncertain, design is usually based on strategies rather than prediction of one exact event.

5.2 Robustness strategies

Four complementary strategies are widely used:

1. Tie forces: provide horizontal and vertical continuity so that members remain connected and loads can be redistributed.
2. Alternate load paths: demonstrate that the structure can bridge over a removed or failed component.
3. Key-element design: protect a component whose failure would cause unacceptable consequences by designing it for a specified abnormal action.
4. Controlled compartmentation or isolation: limit the spread of damage through structural separation, fire protection, or physical barriers.

Codes may require one or more of these strategies according to building use, consequence class, height, and risk category. The selected strategy must be applied consistently to floors, roofs, façades, columns, transfer structures, and foundations.

5.3 Tying

Ties are intended to maintain integrity after local damage. Typical categories include peripheral ties, internal ties, vertical ties, and connections between floors and vertical members. Ties must be continuous through joints and must be anchored into a reliable load path. A tie that terminates at a simple shear connection or an inadequately anchored slab edge does not provide the assumed continuity.

Tie design is not a substitute for member design. After damage, ties may experience large deformation, catenary action, membrane action, or force reversal. Their connections and surrounding members must accommodate these mechanisms without premature fracture.

5.4 Alternate-path analysis

An alternate-path analysis removes or deactivates a notional component and evaluates whether the remaining structure reaches an acceptable state. Typical removals include a column, beam-column segment, or wall segment at representative locations, subject to the governing standard. The analysis may be linear static, nonlinear static, or nonlinear dynamic.

The analysis must include realistic gravity loads, geometric nonlinearity, material nonlinearity where appropriate, connection behaviour, diaphragm action, P–Δ effects, catenary or membrane action when justified, and deformation limits. It should also examine local failure criteria such as connection fracture, bolt tear-out, weld rupture, slab punching, local buckling, and excessive residual deformation.

A simple global equilibrium illustration is useful. If a removed column formerly supported a tributary gravity load P, the adjacent beams may develop flexural resistance and, at larger displacement, catenary tension. The catenary force has a vertical component only when the deformed beam has an inclined geometry. Thus, catenary action cannot be assumed at zero displacement and cannot be mobilized if connections, splices, or surrounding members fail first.

Nonlinear dynamic analysis can capture changing stiffness, contact, force redistribution, and instability more directly, but results depend strongly on modelling assumptions, damping, material laws, fracture criteria, and numerical controls. Sophisticated analysis does not remove the need for engineering judgement or sensitivity studies.

6. Integrated design workflow

A practical workflow is as follows:

Step 1: Define hazards and consequences

Identify wind climate, seismic hazard, soil conditions, flood or impact exposure, fire scenario, occupancy, importance, adjacent structures, and consequences of failure. Establish the governing code and design situations.

Step 2: Establish a three-dimensional structural concept

Select the lateral systems in both directions, locate frames and braces, identify diaphragm lines and collectors, provide a continuous foundation load path, and coordinate openings, stairs, elevators, façades, and services.

Step 3: Build a realistic analytical model

Represent stiffness, mass, releases, diaphragm flexibility, connection rigidity, panel zones, braces, composite action, and foundation restraint at a level appropriate to the design question. Do not assign rigid diaphragms automatically where large openings or flexible decks exist.

Step 4: Analyze wind and seismic actions

Determine code-level forces, modal response where required, torsion, drift, stability effects, diaphragm forces, collector forces, and foundation reactions. Check construction-stage and temporary bracing conditions.

Step 5: Design by hierarchy

Design intended ductile elements and then protect nonductile components through capacity design. Check members, connections, collectors, diaphragms, columns, panel zones, anchors, and foundations for compatible actions.

Step 6: Evaluate robustness

Identify credible local damage scenarios, apply the prescribed removal or abnormal-action procedure, and check alternate paths, ties, deformation, connection integrity, and disproportionate collapse limits.

Step 7: Detail, document, and inspect

Provide drawings showing protected zones, weld requirements, bolt installation, continuity, collectors, diaphragm attachments, erection bracing, inspection categories, and tolerances. A robust design that cannot be reliably built or inspected is not a robust solution.

7. Worked example: preliminary lateral and drift assessment

Consider an illustrative four-story steel building with a rectangular plan. The design seismic weight is W = 12,000 kN. Suppose the applicable code procedure gives C_s = 0.12. The preliminary base shear is

This is a code-level preliminary value, not a final design force until the applicable limits, vertical distribution, accidental torsion, orthogonal effects, and load combinations are checked.

Assume the story heights are 4.0 m and the computed relative displacement at the third story is 42 mm. The interstory drift ratio is

If the relevant code limit for the selected design situation were 2.0%, this preliminary drift would satisfy that particular limit. However, the conclusion would be incomplete unless the designer also checked drift amplification, P–Δ effects, diaphragm deformation, cladding compatibility, nonstructural damage, and drift in the other direction.

Now assume that a first-story column is considered for an alternate-path assessment and that the tributary gravity reaction before removal is 1,000 kN. The adjacent framing cannot simply be assumed to carry 1,000 kN through catenary action. The analysis must establish whether beams can develop flexural resistance, whether joints can rotate, whether ties can sustain the required tension, whether the slab can develop membrane action, and whether columns above and below remain stable. This illustrates why a single reaction value is not a progressive-collapse capacity.

8. Applied case: illustrative irregular office building

Background

An illustrative eight-story office building uses perimeter moment frames and a composite floor deck. A large atrium opening interrupts the floor diaphragm at the centre. Mechanical services also create several penetrations near interior collectors.

Problem

A preliminary model used rigid diaphragms and distributed lateral loads equally to perimeter frames. Review identified three concerns: the atrium caused diaphragm discontinuity, the collector forces were not explicitly designed, and a transfer beam at the lower level supported several columns. The building also had a high-importance occupancy.

Analysis

A revised model represented the diaphragm with in-plane membrane elements, included the atrium boundary, assigned realistic beam-to-column stiffness, and checked collector continuity. Wind torsion increased demand in one perimeter frame. Under seismic loading, the transfer level attracted large force because of stiffness discontinuity. An alternate-path study considered loss of a lower-level column adjacent to the transfer beam.

Approach and solution

The design team introduced a clear collector line around the opening, strengthened deck-to-frame attachments, added diaphragm chord reinforcement, and provided explicit load transfer through the transfer beam connections. The lateral system was modified so that the moment frames had more uniform stiffness. Capacity design was applied to beam-column joints and panel zones, while columns at the transfer level were protected against the probable strength of yielding components. Vertical ties were continued through the affected floors, and the transfer beam and its connections were checked for large deformation and load reversal.

Outcome

The revised model showed improved force distribution and reduced torsional concentration. The alternate-path analysis developed significant beam and slab membrane action without exceeding the prescribed deformation or local-failure criteria. The design team documented the assumptions, inspection requirements, and limits of the analysis rather than presenting the result as proof against every possible abnormal event.

Learning points

The case demonstrates that diaphragm discontinuities can control global response, transfer levels require special attention, rigid-diaphragm assumptions may be unsafe, and robustness depends on continuity through connections and collectors. It also shows that advanced analysis is most valuable when it exposes a load-path problem and leads to constructible detailing.

9. Limitations, governance, and professional responsibility

Lateral and robustness design contains uncertainty in hazard intensity, material properties, damping, connection behaviour, construction quality, deterioration, and human use. Models are representations, not reality. Engineers should identify assumptions, conduct sensitivity checks, use independent review for complex structures, and avoid false precision.

Regulatory compliance is a minimum obligation. Ethical practice also requires protection of occupants, construction workers, emergency responders, neighbours, and future users. Designers should not conceal uncertainty, omit unfavourable load paths, or specify analysis methods beyond their competence. Where a building has unusual geometry, transfer structures, high consequence of failure, or novel devices, peer review and specialist consultation are appropriate.

Quality assurance should cover material certificates, weld procedures, welder qualifications, bolt installation, deck and stud installation, brace geometry, fire protection, corrosion protection, inspection records, and as-built deviations. Digital models should be version-controlled. AI-assisted design or checking may help identify inconsistencies, compare alternatives, or automate repetitive calculations, but it cannot replace code interpretation, engineering judgement, traceable assumptions, or professional responsibility. AI outputs require independent verification, especially for connection behaviour, nonlinear analysis, and abnormal-event scenarios.

10. Contemporary developments and best practice

Current practice is moving toward performance-based design, integrated structural-fire engineering, resilience-based assessment, and improved digital coordination. Important developments include:

• nonlinear response-history analysis for complex seismic systems;
• validated buckling-restrained and replaceable energy-dissipation devices;
• structural-health monitoring using sensors and digital twins;
• probabilistic hazard and consequence assessment;
• low-carbon steel selection and design for disassembly;
• improved fracture and fatigue assessment of welded connections;
• explicit modelling of diaphragm and façade interaction; and
• risk-informed robustness design rather than reliance on a single prescriptive check.

These developments should be adopted selectively. A more complex model is justified only when it addresses a meaningful design uncertainty and can be validated, reviewed, and communicated. Simpler conservative design may be preferable when data or construction control are limited.

Chapter Summary

Wind, seismic, robustness, and progressive-collapse design require a complete and continuous structural load path. Wind pressures produce global shear, overturning, uplift, local component forces, and sometimes dynamic response. Earthquake design is governed by mass, stiffness, strength, ductility, energy dissipation, drift, and cyclic connection behaviour. Moment frames, braced frames, eccentric systems, buckling-restrained braces, and dual systems provide different balances of stiffness, strength, openness, and ductility.

Capacity design protects nonductile components while allowing selected zones to yield. Diaphragms, collectors, ties, connections, columns, and foundations are essential parts of the lateral system. Robustness is achieved through continuity, redundancy, alternate load paths, key-element protection, and control of damage propagation. Progressive-collapse assessment requires realistic modelling of local removal, deformation, nonlinear behaviour, connection integrity, and possible catenary or membrane action.

Good professional practice combines code compliance, appropriate analysis, constructible detailing, inspection, documentation, independent review, and transparent treatment of uncertainty. The objective is not to predict every event but to create a structure that remains stable, repairable, and proportionate in response to credible hazards and local damage.

Key Terms

Ductility: Ability to sustain significant inelastic deformation while retaining useful resistance.

Capacity design: Design method that establishes a hierarchy in which selected components yield before protected components fail.

Diaphragm: Floor or roof system that transfers in-plane lateral forces.

Collector: Element that gathers and transfers diaphragm forces to a vertical resisting system.

Drift: Relative lateral displacement, commonly measured between adjacent floors.

Interstory drift ratio: Story drift divided by story height.

Moment-resisting frame: Frame that resists lateral action mainly through beam-column flexure and connection rotation.

Braced frame: Frame that resists lateral action mainly through axial forces in diagonal braces.

Dual system: Structural system combining two complementary lateral-force-resisting systems.

Redundancy: Availability of multiple components or load paths capable of carrying structural actions.

Robustness: Ability to tolerate localized damage without disproportionate overall damage.

Progressive collapse: Spread of local failure into a larger, disproportionate collapse.

Alternate load path: Redistribution route that carries loads after local component loss.

Tie force: Force-resisting continuity provided by horizontal or vertical structural ties.

Key element: Component specially designed to resist a prescribed abnormal action because its loss has severe consequences.

Catenary action: Tensile mechanism developed by a significantly sagging beam or slab.

P–Δ effect: Additional moment caused by axial load acting through lateral displacement.

Low-cycle fatigue: Damage caused by repeated large-amplitude inelastic strain reversals.

Capacity-protected component: Component proportioned to remain essentially elastic while a designated ductile component yields.

Performance-based design: Design approach that explicitly relates hazard intensity to structural performance objectives.

Review Questions

5 Short Answer Questions

1. What is meant by a continuous lateral load path?
2. Distinguish strength design from drift and serviceability design.
3. Why are collectors important in a diaphragm system?
4. Define capacity design and identify its main purpose.
5. State two differences between robustness and redundancy.

5 Long Answer Questions

1. Explain the behaviour and appropriate applications of moment frames, concentrically braced frames, eccentrically braced frames, and dual systems.
2. Describe how wind and seismic forces travel from cladding or building mass to the foundations.
3. Discuss the connection and detailing requirements for cyclic seismic loading.
4. Explain the principal strategies used to limit progressive collapse.
5. Describe a suitable workflow for integrated wind, seismic, and robustness design of a steel building.

3 Analytical / Application Questions

1. A four-story building has a seismic weight of 15,000 kN and a code response coefficient of 0.10. Calculate the preliminary base shear and explain what additional checks are required before member design.
2. A story is 3.6 m high and has a relative displacement of 54 mm. Calculate the interstory drift ratio and discuss whether the result alone is sufficient to judge performance.
3. Propose an alternate-path assessment for the notional loss of an interior ground-floor column. Identify the modelling assumptions, components to check, likely failure mechanisms, and design strategies that could improve robustness.

Multiple Choice Questions with Answers

Question 1

Which element primarily transfers in-plane lateral forces from a floor to vertical resisting elements?

A. Diaphragm

B. Base plate

C. Column splice

D. Pile cap

Correct Answer: A. Diaphragm

Question 2

A building has seismic weight W = 10,000 kN and response coefficient C_s = 0.08. Using V = C_s W, what is the preliminary base shear?

A. 80 kN

B. 800 kN

C. 8,000 kN

D. 125,000 kN

Correct Answer: B. 800 kN

Question 3

What is the principal objective of capacity design?

A. To make every component yield simultaneously

B. To eliminate all lateral drift

C. To protect selected components while intended ductile zones yield

D. To replace connection design with member design

Correct Answer: C. To protect selected components while intended ductile zones yield

Question 4

A story drift is 36 mm and the story height is 3.0 m. What is the interstory drift ratio?

A. 0.12%

B. 1.2%

C. 8.3%

D. 12%

Correct Answer: B. 1.2%

Question 5

Which system obtains much of its seismic energy dissipation from a designated link beam?

A. Eccentrically braced frame

B. Unbraced gravity frame

C. Simple truss roof

D. Pinned column base system

Correct Answer: A. Eccentrically braced frame

Question 6

Why can a rigid-diaphragm assumption be inappropriate?

A. It always underestimates torsion

B. It ignores possible diaphragm flexibility and discontinuities

C. It prevents any load transfer to braces

D. It eliminates the need for collectors

Correct Answer: B. It ignores possible diaphragm flexibility and discontinuities

Question 7

Which is an alternate-path strategy for robustness?

A. Removing all connections from the model

B. Designing the structure to bridge over a notional failed component

C. Reducing tie continuity

D. Ignoring geometric nonlinearity

Correct Answer: B. Designing the structure to bridge over a notional failed component

Question 8

What is catenary action in a beam or slab?

A. Compression caused by zero displacement

B. Tension developed in a significantly sagging member

C. Shear resistance of a bolt group only

D. Elastic buckling of a brace

Correct Answer: B. Tension developed in a significantly sagging member

Question 9

The expression q_z = ½ρV_z² represents which quantity in wind engineering?

A. Velocity pressure

B. Seismic base shear

C. Plastic moment

D. Interstory drift

Correct Answer: A. Velocity pressure

Question 10

Which statement best describes robustness?

A. The ability to tolerate localized damage without disproportionate collapse

B. The ability to remain completely elastic under every earthquake

C. The use of only one highly strong load path

D. The elimination of all construction tolerances

Correct Answer: A. The ability to tolerate localized damage without disproportionate collapse