Report: 97

Building Type: Medium/high rise moment resisting reinforced concrete frame building

Country: Romania

Author(s): Maria D. Bostenaru

Last Updated:

Regions Where Found: Buildings of this construction type can be found in Romania. According to Balan (1982), 90% of the building stock inRomania at the time of writing, was built after 1950. In Bucharest itself, between 1950 and the earthquake thatoccurred in 1977, a total of around 400,000 new residential apartment units were constructed, and two thirds of thesewere housed in medium rise constructions. Out of the latter about 4% where built using a reinforced concrete framestructure. This type of housing construction is commonly found in urban areas.

Summary: Such buildings generally range from 10 to 17 storeys in height with the ground floor being usedfor commercial purposes, whilst the upper floors house residential units. The vertical loadbearing structure consists of moment-resisting reinforced-concrete frames which also generallyserve as the lateral load-resisting system. However, when larger spans are encountered,reinforced-concrete structural walls are included to provide a dual structural system. Masonryinfills built from lightweight concrete masonry units provide architectural space delineation.The seismic performance of such buildings constructed prior to 1977 varies from no damageto complete collapse. To date damage has usually been attributable to conceptual andconstruction mistakes.

Length of time practiced: Less than 25 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Residential, 20-49 unitsMixed residential/commercial

Typical number of stories: 4-18

Terrain-Flat: Typically

Terrain-Sloped: 3

Comments: After 1990 new buildings were no longer constructed in thearchitectural socialist post-modern style. Two buildings of this latte

Plan Shape: Square, solidRectangular, solidL-shapeU- or C-shape

Additional comments on plan shape: The plan shape can be any shape, but most typically it is either a rectangular, square, L or U layout.

Typical plan length (meters): 12.7-30

Typical plan width (meters): 12-17

Typical story height (meters): 2.75

Type of Structural System: Structural Concrete: Moment Resisting Frame: Designed for gravity loads only, with URM infill walls

Additional comments on structural system: The vertical load-resisting system is reinforced concrete moment resisting frame. Monolithic cast in-situ reinforcedconcrete slabs transfer the gravity loads to the reinforced concrete beam and column framing down to the foundation.Various architectural requirements give rise to particular cases, such as where window openings result in the beamsbeing cast as up-stands rather than down-stands. Furthermore, in some cases brick masonry infills might actually carry some local vertical load.The lateral load-resisting system is reinforced concrete moment resisting frame. The main lateral load resisting systemis provided by the reinforced concrete moment resisting frames. The infills then, although notaccounted for in design, invariably contribute to the building's stiffness. The use of a higher storey height for the lowerfloor for commercial purposes gives rise to an increased likelihood of a soft storey mechanism.

Gravity load-bearing & lateral load-resisting systems:

Typical wall densities in direction 1: 5-10%

Typical wall densities in direction 2: 5-10%

Additional comments on typical wall densities: The typical structural walldensity is up to 10 %. The above values are for the (lightweight concrete) infill walls.

Wall Openings: Openings areformed in the masonry infill (see fig. 2,2B and 2C). Since the masonry infill is usually out of light concrete (betoncelular autoclavizat), the position and size of openings is not generally considered to influence the structuralcharacteristics at the design stage.

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

Modifications of buildings: The light partition/infill walls have allowed for numerous modifications to the interior spaces of these buildingswithout directly influencing the geometrical characteristics of the main reinforced concrete structural members. After1990 many facades of these constructions have been modified with balconies being closed off and included in the glassand metal facade structures installed.

Type of Foundation: Shallow Foundation: Mat foundation

Additional comments on foundation: Probably other foundation forms are encountered, such as piles in certain cases.

Type of Floor System: Other floor system

Additional comments on floor system: Solid slabs (cast-in-place); Solid slabs (precast)

Type of Roof System: Roof system, other

Additional comments on roof system: Solid slabs (cast-in-place); Solid slabs (precast)

Additional comments section 2:

Who is involved with the design process? EngineerArchitect

Roles of those involved in the design process: The architectural plans are developedby architects. Structural design and construction supervision is typically carried out by engineers.

Expertise of those involved in the design process: State enterprises provide all professional architectural and engineering services.

Who typically builds this construction type? BuilderOther

Roles of those involved in the building process: The builder does not typically live in this construction type as they were not built by developers but by stateenterprises.

Expertise of those involved in building process:

Construction process and phasing: Little data are available, apart from the obvious steps in constructing an RC framed building. Theconstruction of this type of housing takes place in a single phase. Typically, the building is originally designed for itsfinal constructed size.

Construction issues:

Is this construction type address by codes/standards? Yes

Applicable codes or standards: This construction type is addressed by the codes/standards of the country. P.13-70. The year the firstcode/standard addressing this type of construction issued was 1970. The most recent code/standard addressing thisconstruction type issued was 1992. March1977: new seismic zonation (decree 66) > new zonation standard in 1978. March 1977: publishing for publicdiscussion the project of the law nr. 8 regarding the durability, the safety in usage, functionality and quality ofconstructions > new anti-seismic design code (normative): P.100-78, later improved in P.100-1981, containing newprescriptions regarding the set-up of cast-in-place and precast reinforced concrete, metal and masonry constructions. Ittook in consideration the new zonation, and accentuated the reduction of construction weight, and the rational shapeof the assembly, computing coefficients were changed, the computing of displacements prescribed in order to avoidpounding damage, ductility was desirable, and also the execution conditions were prescribed (work phases).Documents were made immediately after the earthquake also regarding reparation measures (technical instructions).The document from 1981 did not bring radical modifications, but more precision (regarding the dynamic coefficientdepending on local site conditions, limits of relative displacements and the way to evaluate these, computing methodsfor eccentricity etc). The main completions regard installations and an annex considering spatial oscillations.

Process for building code enforcement: There used to be a quality control organization, CTC (Control Tecnic de Calitate services).

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)

Additional comments on maintenance and building condition:

Unit construction cost: No available data.

Labor requirements: No available data.

Additional comments section 3:

Patterns of occupancy: One family occupies a single flat.Each building typically has 30 housing unit(s).

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: Middle-income class

Additional comments on economic level of inhabitants:

Typical Source of Financing: Government-owned housingOther

Additional comments on financing: Originally the buildings were constructed with government financing and then rented out. The tenants later had theopportunity to buy their apartment at a favorable price, given that they had rented them for a certain amount oftime.

Type of Ownership: RentUnits owned individually (condominium)

Additional comments on ownership:

Is earthquake insurance for this construction type typically available?: Yes

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?: Yes

Additional comments on premium discounts:

Additional comments section 4: According to “Magazinul Romnesc” 2% of the residences were earthquake assured by the timeof the 2004 earthquake. According to “Magazinul Romnesc” the insurance costs 0,3-0,5% of the value of theresidence.

Damage patterns observed in past earthquakes for this construction type: According to Balan (1982), during the 1977 earthquake, damage was typically concentrated locally in the reinforcedconcrete columns and beams on the ground floor and up to the fourth storey. Furthermore, severedamage to the masonry infill walls was evidenced as well.

Additional comments on earthquake damage patterns: Weak storey: slender columns, concrete spalling, buckling of thereinforcement in plastic hinge locations. Central andshort columns suffer, stirrup rupture, column dislocation, cracks,brittle failures especially at the intersection with staircases which giverise to a captive column effect. Typical storeys: In the columns,horizontal cracks directly under/over the beams, orthogonally to thecolumn axis, concrete spalling, buckling of the reinforcement bars atplastic hinges, inclined X-shaped cracks. In thebeams, larger span beams suffer from concrete spalling in the plastichinge zones. Cracks in the beam-column connections. Inshorter span beams, inclined cracks on the lower half of the beams.Inclined X-shaped cracks, vertical flexural cracks in secondary beams. Superficial cracks in the plastering, separation cracks on the perimeter.Inclined X-cracks, sliding failure in the first storey and atconstruction joints, partial or complete failure of the masonry, deformation of the window frames with glass breakages, cracksin the lintels, disintegration of the partition walls especially whereconstruction joints are present. Cracks in the lower storeys, at interaction with central and shortcolumn.

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.

Additional comments on structural and architectural features for seismic resistance:

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls:

Earthquake-resilient features in walls:

Seismic deficiency in frames: Where commercial premises are housed a softstorey mechanism can be prevalent, due to thelarger storey heights and possible larger spans. During the structural design,the influence of the masonry infills is not takeninto account. The amount of reinforcement inthe main structural members is not alwaysexactly prescribed. The detailing of the beam-columnconnections. Poor construction materialquality, mistakes during construction, such asout-of-plumb columns. Where precast structuralmembers are used the connections are a causeof concern.

Earthquake-resilient features in frame: A regular andthree dimensionalcolumn grid givingrise to a robustmoment resistingspatial framesystem. In somebuildingsstructuralreinforcedconcrete walls areincorporated togive rise to a dualsystem.

Seismic deficiency in roof and floors:

Earthquake resilient features in roof and floors: Stiff cast in-situ 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:

Has seismic strengthening described in the above table been performed? Yes.

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? Following the 1977 Vrancea earthquake, various repairs were carried out. Nowadays buildings are being retrofitted as amitigation measure

Was the construction inspected in the same manner as new construction? No.

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? Contractors performed the construction and both architecture and engineering institutions were involved.

What has been the performance of retrofitted buildings of this type in subsequent earthquakes? The performance was good but the subsequent earthquakes were weaker.

Additional comments section 6:

• “The 1977 March 4, Earthquake in Romania” (in RomaM. Lupan

• “Economic Efficiency and Applicability of BuildingMaria Bostenaru Dan

• “At a degree from disaster” (in Romanian). In: Mag

• Karl Steinbrugge collection