Reinforced concrete frame wall building ,USA

From World Housing Encyclopedia


1. General Information

Report: 98

Building Type: Reinforced concrete frame wall building without seismic details

Country: United States of America

Author(s): Craig Comartin, Kenneth Elwood

Last Updated: 7/11/2004

Regions Where Found: This housing type can be found in most urban areas across the country, including California. Percentage of housing stock unknown, but expected to vary based on region.

Summary: While this building type is predominantly used for office space and hotels, it is also used in urban areas for multi-family dwellings (condominiums) and university dormitories. It can be found in most urban areas across the country. In California, this building type was constructed prior to the requirements for seismic details, introduced into local building codes in the early 1970's. These buildings are vulnerable to numerous failure modes including: failure of lap splices in wall boundary elements and columns; punching shear failures in flat plate slabs; and shear and axial load failure of columns with wide transverse reinforcement spacing. A discontinuity in stiffness and strength at the lower stories, due to discontinuous shear walls for example, normally results in a concentration of earthquake damage in these stories. This form will concentrate on frame-wall buildings found in California, although the description may apply to similar buildings across the country.

Length of time practiced: < 75 years

Still Practiced: No

In practice as of:

Building Occupancy: Multi-unit, unknown type

Typical number of stories: 4 - 10

Are buildings of this type typically built on flat or sloped terrain? Flat terrain only.

Comments: This construction type is still being practiced in regions of low seismic risk, but not in high seismic risk regions like California.


2. Features

Plan Shape: Rectangular, solid

Additional comments on plan shape: Most are rectangular, or nearly rectangular, but can be found in many different building configurations.

Typical plan length (meters): 35-45

Typical plan width (meters): 20-30

Typical story height (meters): 3

Type of Structural System: Concrete: Moment resisting frame: Designed for gravity loads only (predating seismic codes i.e. no seismic features), Flat slab structure, Frame with concrete shear walls-dual system; Concrete: Shear wall structure: Walls cast in-situ

Additional comments on structural system:

Gravity load-bearing & lateral load-resisting systems: Concrete frame-wall buildings typically possess a complete gravity frame system, essentially independent of the concrete walls, to support vertical loads. However, in some instances concrete walls may carry some local vertical gravity loads. The buildings in this category generally have monolithically cast-in-place reinforced concrete horizontal floor and roof systems. Various concrete floor and roof framing systems used with this building type include flat plate, pan joist or beam, one-way slab, and two-way slab or waffle slab systems.

Concrete frame-wall buildings can include, for example, exterior perforated walls with short piers and deep spandrels, interior concrete walls near stair and elevator cores, or perimeter frames with concrete infill walls. In these buildings, walls provide all or most of the lateral force resisting systems. The layout of wall locations was, to a large part, dictated by functional considerations. In many older buildings this was the only consideration, resulting in floor plans that induce torsion. Perimeter walls typically contain numerous window and door openings. In multistory buildings, the openings were frequently arranged in a regular grid. This pattern of openings gives rise to the pier and spandrel system composed of relatively deep spandrel beams and relatively short and wide wall piers.

Typical wall densities in direction 1: 0-1%

Typical wall densities in direction 2: 0-1%

Additional comments on typical wall densities: 0.023 in transverse direction 0.025 in longitudinal direction

Wall Openings: Info not provided in the report.

Is it typical for buildings of this type to have common walls with adjacent buildings?: yes

Modifications of buildings: Not provided in the report.

Type of Foundation: Shallow Foundation: Reinforced concrete isolated footing, Reinforced concrete strip footing

Additional comments on foundation: None.

Type of Floor System: Structural Concrete, cast in place flat slab.

Additional comments on floor system: None.

Type of Roof System: Structural Concrete, cast in place flat slab.

Additional comments on roof system: None.

Additional comments section 2: None.


3. Building Process

Description of Building Materials

Structural Element Building Material (s) Characteristic Strength Comment (s)
Walls Concrete; Reinforcement 17 MPa; 275 MPa None
Foundations Concrete; Reinforcement 17 MPa; 275 MPa None
Frame Concrete; Reinforcement 20 MPa; 275 MPa None
Roof and floors Concrete; Reinforcement 17 MPa; 275 MPa None

Design Process

Who is involved with the design process? 7.6

Roles of those involved in the design process: 7.6

Expertise of those involved in the design process: 7.4


Construction Process

Who typically builds this construction type? Builder

Roles of those involved in the building process: Standard construction equipment was used. Wood forms were used almost exclusively. Concrete may be pumped for upper stories.

Expertise of those involved in building process: Most buildings of this type were constructed to the state-of-practice (code level) of the time. Given the general lack of knowledge of building behavior during earthquakes at the time, engineers and contractors cannot be faulted for lack of expertise.

Construction process and phasing: Building originally designed for its final constructed size

Construction issues: Not provided in the report.


Building Codes and Standards

Is this construction type address by codes/standards? yes

Applicable codes or standards: Title of the code or standard: ACI 318 or UBC prior to early 1970's;

National building code, material codes and seismic codes/standards: Building code for California and seismic code - Uniform Building Code Materials code - ACI 318;

When was the most recent code/standard addressing this construction type issued? type of construction has not been allowed by the building code since the early 1970's (depending on local adoption of the 1973 UBC).

Process for building code enforcement: Professional engineer stamps drawings, certifying that they meet code requirements. In the field, the resident engineer inspects construction to ensure it conforms with the design drawings. Local building officials may also inspect during or after construction to ensure compliance with local codes.


Building Permits and Development Control Rules

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: None.


Building Maintenance and Condition

Typical problems associated with this type of construction: Not provided in the report.

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

Additional comments on maintenance and building condition: None.


Construction Economics

Unit construction cost: Per m2 of built-up area expressed using a currency used in the region, and, if possible, an equivalent amount in $US in the brackets e.g. 200 Rs/m2 (5 $US/m2).

Labor requirements: Number of effort days required to complete the construction

Additional comments section 3: None.


4. Socio-Economic Issues

Patterns of occupancy: One family per housing unit,

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: None.

Economic level of inhabitants: Middle-income class

Additional comments on economic level of inhabitants: None.

Typical Source of Financing: Owner Financed, Commercial banks / mortgages

Additional comments on financing: None.

Type of Ownership: Rent, Units owned individually (condominium)

Additional comments on ownership: None.

Is earthquake insurance for this construction type typically available?: Info Not provided in the report.

What does earthquake insurance typically cover/cost: -

Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features?: -

Additional comments on premium discounts: None.

Additional comments section 4: None.


5. Earthquakes

Past Earthquakes in the country which affected buildings of this type

Year Earthquake Epicenter Richter Magnitude Maximum Intensity
1994 Northridge, CA 6.7 MMI IX
1989 Loma Prieta, CA 7.1
1979 Imperial Valley, CA 6.4
1971 San Fernando, CA 6.6

Past Earthquakes

Damage patterns observed in past earthquakes for this construction type: Walls: Concentration of damage at “weak story” with discontinuous shear walls. Diagonal shear cracking in coupling beams and piers. Diagonal shear cracking at base of wall. Crushing of concrete at toe of wall. Buckling of longitudinal boundary reinforcement. Frame (Columns, beams): If walls not stiff enough to limit displacements, shear failures expected (severe diagonal cracking).Axial failure may follow. Roof and floors: Cracking at wall-slab construction joints. Punching shear failure at columns.

Additional comments on earthquake damage patterns: None.


Structural and Architectural Features for Seismic Resistance

Structural/Architectural Feature Statement Seismic Resistance
Lateral load path The structure contains a complete load path for seismic force effects from any horizontal direction that serves to transfer inertial forces from the building to the foundation. FALSE
Building Configuration-Vertical The building is regular with regards to the elevation. (Specify in 5.4.1) TRUE
Building Configuration-Horizontal The building is regular with regards to the plan. (Specify in 5.4.2) TRUE
Roof Construction The roof diaphragm is considered to be rigid and it is expected that the roof structure will maintain its integrity, i.e. shape and form, during an earthquake of intensity expected in this area. TRUE
Floor Construction The floor diaphragm(s) are considered to be rigid and it is expected that the floor structure(s) will maintain its integrity during an earthquake of intensity expected in this area. TRUE
Foundation Performance There is no evidence of excessive foundation movement (e.g. settlement) that would affect the integrity or performance of the structure in an earthquake. TRUE
Wall and Frame Structures-Redundancy The number of lines of walls or frames in each principal direction is greater than or equal to 2. TRUE
Wall Proportions Height-to-thickness ratio of the shear walls at each floor level is: Less than 25 (concrete walls); Less than 30 (reinforced masonry walls); Less than 13 (unreinforced masonry walls); TRUE
Foundation-Wall Connection Vertical load-bearing elements (columns, walls) are attached to the foundations; concrete columns and walls are doweled into the foundation. TRUE
Wall-Roof Connections Exterior walls are anchored for out-of-plane seismic effects at each diaphragm level with metal anchors or straps. TRUE
Wall Openings The total width of door and window openings in a wall is: 1) for brick masonry construction in cement mortar: less than 1/2 of the distance between the adjacent cross walls; 2) for adobe masonry, stone masonry and brick masonry in mud mortar: less than 1/3 of the distance between the adjacent cross walls; 3) for precast concrete wall structures: less than 3/4 of the length of a perimeter wall N/A
Quality of Building Materials Quality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). TRUE
Quality of Workmanship Quality of workmanship (based on visual inspection of a few typical buildings) is considered to be good (per local construction standards). TRUE
Maintenance Buildings of this type are generally well maintained and there are no visible signs of deterioration of building elements (concrete, steel, timber). FALSE

Additional comments on structural and architectural features for seismic resistance: None.

Vertical irregularities typically found in this construction type: Not provided in the report.

Horizontal irregularities typically found in this construction type: Not provided in the report.

Seismic deficiency in walls: Discontinuous shear walls at lowest levels. Boundary elements not confined. Vertical lap splices not designed for overturning tensile forces. No anchorage for horizontal reinforcement. Cannot develop flexural capacity (i.e. shear critical)Minimal reinforcement around openings. No ductile detailing in coupling beams. Inadequate connection between walls and foundations. Foundation settlement under walls during lateral loading increases displacement demands on frame system. Irregular layout of walls can result in higher demands due to torsional effects.

Earthquake-resilient features in walls: Resilient to gravity load collapse. Provides stiffness which reduces the displacement demands on columns of frame system.

Seismic deficiency in frames: Columns: Large transverse reinforcement spacing. 90-deg hooks on transverse reinforcement. Lap splices at floor levels. Shear capacity less than shear required to form plastic hinges.

Earthquake-resilient features in frame: Will not resist substantial lateral loads but must maintain gravity loads.

Seismic deficiency in roof and floors: Drag struts not provided at re-entrant corners. Slabs doweled into walls with no hook provided for bottom reinforcement. Dowels not sufficient to develop yield yield strength, or strength of diaphragm. Insufficient shear strength at columns.

Earthquake resilient features in roof and floors: Slab reinforcement may be sufficient to handle corner stresses.

Seismic deficiency in foundation: Not provided in the report.

Earthquake-resilient features in foundation: Not provided in the report.


Seismic Vulnerability Rating

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

High vulnerability Medium vulnerability Low vulnerability
A B C D E F
Seismic vulnerability class < >

Additional comments section 5: None.


6. Retrofit Information

Description of Seismic Strengthening Provisions

Structural Deficiency Seismic Strengthening
Soft or Weak Story Soft or weak stories are the most common deficiencies in buildings of this type.

Additional comments on seismic strengthening provisions:

Has seismic strengthening described in the above table been performed? Yes. Many of these strengthening techniques have been applied to institutional buildings (e.g. universities) throughout California.

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? The purpose of the retrofit was for mitigation.

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

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? An engineer designed the retrofit and a contractor performed the construction.

What has been the performance of retrofitted buildings of this type in subsequent earthquakes? No subsequent earthquakes have tested these retrofit techniques.

Additional comments section 6: None.


7. References

  • ATC 40, 1996, “Seismic Elvaluation and Retrofit of Concrete Buildings”, Applied Technology Council, Volumes 1-2.

Authors

Name Title Affiliation Location Email
Craig Comartin President Comartin-Reis 7683 Andrea Avenue Stockton, CA, 95207-1705 United States of America comartin@comartin-reis.com
Kenneth Elwood Assistant Professor University of British Columbia 2324 Main Mall Vancouver V6T1Z4 BC Canada elwood@civil.ubc.ca
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