High-Rise Building Lateral Loads Resisting System Types

Explain how high-rise buildings are defined by fire safety and evacuation considerations, using 23 meters as a threshold per NFPA and IBC, not by stories.

Identify the primary lateral loads on high-rise buildings as earthquake and wind loads, and analyze how stiffness, mass, and natural frequency govern resonant response to long-period seismic waves.

The period is the time for one full vibration cycle, and frequency is the number of cycles per second, with high-rise buildings having longer periods and resonance.

Explore how wind loads affect tall buildings, with along-wind pressures and transverse vibrations from vortex shedding, leading to low-frequency resonant concerns and design implications for high-rise systems.

Understand the flat slab with columns as a primary lateral-load system up to about 10 stories, its limited energy dissipation, and the need to reinforce the column-slab connection.

Apply Gruzman method to compute the effective width of slabs for lateral load resistance, using CD factor, drift limits, and column geometry; compare with Gang and Dweller's method.

Use the Kang & Wallace method to compute effective width for flat-slab systems from shake-table data, with alpha 2.75, beta about 2.3, and Z strip tied to center-line spacing.

Use the Hwang and Moehle method to determine effective width with a finite-element based solution, noting square-section limits, center-to-center bay distances, and stiffness reductions for Z sections.

Explain the British code method for effective width using centerline to centerline of the bay, and note that four methods will be illustrated in the next lecture.

Evaluate slab contribution to lateral loads in high-rise flat-slab column systems using Grossmann, King and Wallace, Wangan, Modie, Mesud, and the British code for interior and exterior bays.

Compare the equivalent frame method with finite element analysis; finite element modeling yields higher stiffness and lower displacement and drift, while the equivalent method remains conservative for approximate lateral-load analysis.

Explore dual system of shear walls and flat slabs for seismic zones C–F, noting effective width is column width plus 1.5 slab thickness and frames resist 25% of seismic loads.

Explore the shear walls and frames dual system, a high-rise mainstay that blends concrete in compression with steel in tension to resist wind and seismic forces.

Explore how coupled shear walls joined by a pendrel beam restrain cantilever bending and make two walls act as one unit in high-rise buildings.

Design of the coupling beam governs the coupling shield wall behavior. Use the clear length to depth ratio to decide between diagonal reinforcement, Lebanon reinforcement, or special moment resisting frame.

Explore how different high-rise lateral load resisting systems affect displacement, including flat slabs with drop panels or perimeter beams, ductile frame, and Schierholz, under seismic loading.

Explore the DeGroot diagonal grid lateral system, which removes vertical columns to create a diamond façade; first used in the 1965 IBM building and revived in the early 2000s.

Examine how a diagrid's diagonals and ring beams form triangles that carry wind and seismic loads via axial compression and tension, with node connections and diagonal inclination shaping load distribution.

Identify the gravity load path through the grid, with vertical loads traveling along diagonals to the ring beam; diagonals carry compression, the ring beam carries tension.

Examine how wind loads transfer in high-rise lateral systems, detailing overturning moment and shear, and how diagonals and ring members carry compression and tension.

Concentrated loads on floors intersecting the diagonals create reactions on the diagonal, producing bending moments and axial forces while resolving the load into components parallel and perpendicular to the diagonal.

Describe diagrid system components, including factory-fabricated nodes delivered onsite, diagonals of circular hollow sections, ring beams of rectangular or square hollow sections, and welded or bolted joints based on exposure.

Evaluate the advantages and disadvantages of the grid system for high-rise lateral load resistance, highlighting light access, leed benefits, cost reductions, and construction challenges.

Explore how outrigger systems enhance high-rise stability by coupling the core with external arms to reduce core deflection and moments, while increasing stiffness but not shear resistance.

Use belt walls with outriggers to create a restoring moment that reduces core moment and displacement, and if possible, integrate external built beams or trusses to restrain the perimeter columns.

Determine optimum outrigger locations from architectural plans and mechanical coordination. Use mid-height for a single outrigger; one-quarter, half, and three-quarters for three outriggers to maximize drift reduction.

Examine how the framed tube system uses the building perimeter as a cantilever to resist lateral loads, with columns linked by Pendrell beams and a hollow tube cross section.

Explore the framed tube system, where perimeter columns tied by rigid beams resist lateral loads as a cantilever. Understand how shear lag and corner-column stresses differ from solid shear walls.

Explore the braced tube system as the first modification to overcome shear lag and reduce axial stresses on columns, increasing spacing and enabling taller buildings up to 100 floors.

The bundled tube system stacks tubes at different levels to reduce shear lag, increase column spacing, confuse wind, and resist vortex shedding up to 120 floors.

Explore how columns shorten under compression in high-rise buildings, highlighting elastic shortening for steel and concrete, creep and shrinkage for concrete, and the relative shortening between exterior and interior columns.

Analyze the effects of relative column shortening in a high-rise with a central core, illustrating the umbrella shape, impacts on slabs and outriggers, and cracks and deformations.

Learn how to compensate column shortening in tall buildings using the over cost technique, addressing pre-costing and after-costing effects in concrete and steel structures.

Explore the final overview of lateral load resisting systems for tall buildings, including rigid frames, Schierholz diagramed systems, outriggers, and tube structures.