Report: 3

Building Type: Steel frame buildings with shear walls

Country: Chile

Author(s): Elias Arze L.

Last Updated:

Regions Where Found: Buildings of this construction type can be found in mainly large cities like Santiago, Concepcion, Valdivia, Temuco, Villarrica. Percentage of total area built is below 2 %. This type of housing construction is commonly found in urban areas.

Summary: These buildings are modern steel composite structures ranging from 3 to 24 stories. The buildings have a rigid steel frame with floor diaphragms made of post-tensioned concrete slabs or composite steel decking, with or without a concrete slab covering. Additional lateral force-resisting elements are added to the steel moment-resisting frame to stiffen the structure and enhance the seismic performance. These elements are steel #X# or concentric braces and reinforced concrete shear walls. The seismic performance for these composite structures is very good. Most of these buildings are used as apartments or offices.

Length of time practiced: 76-100 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Residential, 50+ units

Typical number of stories: 3 to 5 and 6 to 24

Terrain-Flat: Typically

Terrain-Sloped: Off

Comments: This construction type has been used since 1965-70. Some buildings include commercial ground floor too.

Plan Shape: Rectangular, solid

Additional comments on plan shape:

Typical plan length (meters): 10-20

Typical plan width (meters): 20-30

Typical story height (meters): 3

Type of Structural System: Steel: Moment Resisting Frame: With cast in-situ concrete walls

Additional comments on structural system: The vertical load-resisting system is steel braced frame. Steel deck slabs, prestressed concrete slabs, reinforced concrete slabs. Steel beams, normally composite. Steel columns and shear walls. The lateral load-resisting system is steel structural walls. Dual construction, shear walls combined with rigid steel frame. Up to 5 stories x or v or ^ braced shear walls. Over 5 stories - reinforced concrete slip or jump formed walls.

Gravity load-bearing & lateral load-resisting systems: Typical buildings have shear wall, light weight partitions and some concentric brace frames.

Typical wall densities in direction 1: 1-2%

Typical wall densities in direction 2: 1-2%

Additional comments on typical wall densities:

Wall Openings: 20 to 30%

Is it typical for buildings of this type to have common walls with adjacent buildings? No

Modifications of buildings:

Type of Foundation: Shallow Foundation: Reinforced concrete isolated footingShallow Foundation: Reinforced concrete strip footingShallow Foundation: Mat foundationDeep Foundation: Reinforced concrete bearing pilesDeep Foundation: Steel bearing pilesOther Foundation

Additional comments on foundation: It consists of reinforced concrete end-bearing piles and steel end-bearing piles. Reinforced concrete isolated footing. Reinforced concrete strip footing. Mat foundation. Reinforced concrete bearing piles. Steel bearing piles. Floating deep foundations.

Type of Floor System: Composite steel deck and concrete slabOther floor system

Additional comments on floor system: Other: Post-tensioned slabs, composite steel deck without concrete slab. Floors and roofs are considered as rigid diaphragms

Type of Roof System: Composite steel roof deck and concrete slabRoof system, other

Additional comments on roof system: Other: composite steel deck without concrete slab. Floor and roof are considered as rigid diaphragm.

Additional comments section 2: Buildings are widely spaced, at a minimum of 10 meters.

Who is involved with the design process? EngineerArchitectOther

Roles of those involved in the design process: Developer hires architects, engineers and construction firms. Architects and engineers must visit the job and provide general supervision. They usually must approve construction contracts.

Expertise of those involved in the design: Architects have 5 university years and typically over 5 years of experience. Engineers have 6 university years and typically over 5 years of experience. Construction companies are headed by engineers or architects. Experience about 10 years. The same for fab shops. In steel frame buildings, review of design and independent inspection are typical.

Who typically builds this construction type?: Other

Roles of those involved in the building process: Developer hires architects, engineers and construction firms.

Expertise of those involved in building process: Construction companies are headed by engineers or architects. Experience about 10 years. The same for fab shops. In steel frame buildings, review of design and independent inspection are typical.

Construction process and phasing: Construction of this type typically takes place over time, buildings are originally designed for their final constructed size.

Construction issues:

Is this construction type address by codes/standards? Yes

Applicable codes or standards: Chilean seismic codes NCh433.Of96 & NCh2369 are mandatory. AISC and ACI codes corrected to meet seismic codes are applied. Code/standard addressing this type of construction was first issued 1957. National building code, material codes and seismic codes/standards: NCh433.Of96, seismic design for buildings; NCh2369.Of01 seismic design of industrial buildings, NCh428.Of57code design for steel structures. Most recent code/standard addressing this construction type was issued: 1957, but now there is a draft to modify that code that partially follows AISC and AISI.

Process for building code enforcement: Design review by peers (may belong to design firm) is normal. Independent inspection is normal in steel framed buildings.

Are building permits required? Yes

Is this typically informal construction? No

Is this construction typically authorized as per development control rules? Yes

Additional comments on building permits and development control rules:

Typical problems associated with this type of construction:

Who typically maintains buildings of this type? Owner(s)Renter(s)

Additional comments on maintenance and building condition:

Unit construction cost: Low cost apartments, up to 5 floors, UF 10/sq m (US $300/sq m). Normal, up to 5 floors, UF 20/sq m (US $600/sq m). High-rise, 30/sq m (US$ 900/sq m).

Labor requirements: 1.5 to 2.5 floors per month.

Additional comments section 3:

Patterns of occupancy: One family per unit. Each building typically has 51-100 housing unit(s). For buildings up to 5 floors: 15 - 20 units. For those up to 20 floors: 150 - 200 units.

Number of inhabitants in a typical building of this construction type during the day: >20

Number of inhabitants in a typical building of this construction type during the evening/night: >20

Additional comments on number of inhabitants:

Economic level of inhabitants: Low-income class (poor)Middle-income classHigh-income class (rich)

Additional comments on economic level of inhabitants: House Price/Annual Income ratio: Poor: 4.0 - 4.5, Middle Class: 2.5 - 3.0, Rich: 2.5 - 3.0 Ratio of housing unit price to annual income: 1:1 or better

Typical Source of Financing: Owner financedPersonal savingsCommercial banks/mortgagesOther

Additional comments on financing: Ministry of Housing gives low interest loans for poor or low middle class owners.

Type of Ownership: RentOwn with debt (mortgage or other)Units owned individually (condominium)Owned by group or pool

Additional comments on ownership: Some buildings may belong to an institution

Is earthquake insurance for this construction type typically available? Yes

What does earthquake insurance typically cover/cost: Repairs to same conditions before the earthquake. Occasionally, time lost.

Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features? No

Additional comments on premium discounts:

Additional comments section 4: It is on average. Up to 5 floors, 15-20 units. Up to 20 floors, 150-200

Damage patterns observed in past earthquakes for this construction type: There were many connections of the type that failed in Northridge, Loma Prieta and Kobe. No damage in any of them. Probable causes: # Chilean Building Code allows maximum drift about 1/2 of USA. # Periods are approximately 0.05N instead of 0.1N (N=floors) # No jumbo W sections are used # Beams and columns are welded to stress relieved plates. A good example of good behavior are the seven 4 story-buildings from Poblacion Republica Popular China, located in Vina del Mar. They are 46 X 10.6 m in plan, have moment resisting frames in both directions and 12 cm reinforced concrete slab. In the longitudinal direction the span is 4.6 cm. The buildings were designed according to NCh428.Of 57 with A42-27ES steel.

Additional comments on earthquake damage patterns: No damage in serious earthquakes in 1960 (M9.5) and in 1985 (M7.8)

The main reference publication used in developing the statements used in this table is FEMA 310 “Handbook for the Seismic Evaluation of Buildings-A Pre-standard”, Federal Emergency Management Agency, Washington, D.C., 1998.

The total width of door and window openings in a wall is: For brick masonry construction in cement mortar : less than ½ of the distance between the adjacent cross walls; For adobe masonry, stone masonry and brick masonry in mud mortar: less than 1/3 of the distance between the adjacent cross walls; For precast concrete wall structures: less than 3/4 of the length of a perimeter wall.

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls: None

Earthquake-resilient features in walls: Regular buildings in plan and height good design and construction practice

Seismic deficiency in frames: None

Earthquake-resilient features in frame:

Seismic deficiency in roof and floors: None

Earthquake resilient features in roof and floors:

Seismic deficiency in foundation:

Earthquake-resilient features in foundation:

For information about how seismic vulnerability ratings were selected see the Seismic Vulnerability Guidelines

Additional comments section 5

Additional comments on seismic strengthening provisions: It has not been required in steel framed buildings

Has seismic strengthening described in the above table been performed?:

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages?:

Was the construction inspected in the same manner as new construction?:

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved?:

What has been the performance of retrofitted buildings of this type in subsequent earthquakes?:

Additional comments section 6:

• Edificios de Acero J.Monge, S.Campino, and R.Sharpe a Chapter in “El Sismo de Marzo 1985, Chile”, (Ed.) J.Monge 1985