shepherd park library earthquake damage building waterproofing assessment · 2016-02-01 ·...

SPL STRUCTURAL & WATERPROOFING ASSESSMENT

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SHEPHERD PARK LIBRARY Earthquake Damage & Building Waterproofing Assessment

7420 Georgia Ave. NW Washington DC 20012

COMBINED REPORT

January 22, 2015

INCLUDES

INITIAL STRUCTURAL & WATERPROOFING ASSESSMENT 10/10/14

ADDITIONAL WATERPROOFING SURVEY

11/18/14

FINAL ROOF SURVEY 11/26/14

GDG The Georgetown Design Group, Inc.

1920 N Street, NW, Suite 100, Washington, DC. 20036 (202) 857-0060

www.gdgdesignbuild.com


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Shepherd Park Library Earthquake Damage & Building Waterproofing Assessment


10/10/14

STRUCTURAL EVALUATION

I. EVALUATION SUMMARY This structural and waterproofing assessment of the Shepherd Park Library was conducted by GDG

in association with Structron Engineering LLC. The structural system was examined and evaluated per the information obtained from the original building drawings together with visual surveys of the building conducted to determine the building’s present structural and waterproofing conditions.

The building was found to be generally structurally sound and in good condition but the assessment

also identified some structural and waterproofing defects. The issues will probably not cause immediate structural problems, but remedial work must be done to help avoid further damage. A complete report of findings and recommendations is provided below.

II. METHODOLOGY

1. Process Review of Existing Data A thorough review of all the pertinent data related to the building was accomplished during the evaluation process to determine the conditions of the existing structure and waterproofing system and the causes of the identified defects.

Documents

Existing site plan and Architectural sheets A-2 to A-16 dated 11/20/1987. Prepared by Bryant Associates, P.C

Existing structural design drawing S-1 to S-9 dated 11/20/1987 prepared by Bryant Associates, P.C.

Report and communications from Hill International dated 3/9/2011 and 5/6/2011. Roof repair drawings and specifications dated 5/25/2011 prepared by ECS LLC. Water leaks evaluation report dated 09/16/2013 prepared by Robert Silman Associates. Memorandum dated 1/2/2013 prepared by Lisa Deanes, DCPL.

Condition Surveys Following an initial site visit, two condition assessment surveys were conducted for the purpose of identifying defects and their causes. The surveys involved the visual examination of existing exposed exterior masonry wall, staircase walls, visible structure, and roof areas.

First site visit: April 1, 2014 Preliminary site evaluation: May 14, 2014


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First detailed site survey: August 27, 201. Final site survey: September 12, 2014.

2. Exclusions

The surveys were not invasive in nature and existing concealed concrete framing slabs were therefore not inspected. Likewise, structural steel members that are either encased in masonry or covered by fireproofing, or concealed in ceilings were also not inspected.

3. Codes & Regulations

20012 IBC Concrete- “Standard Building code Requirement for Reinforced concrete” of ACI. Structural Steel – “Specification for the Design, Fabrication, and Erection Of Structural

steel for Building” of AISC. Concrete Block Masonry – “Specification of the design and construction” of N.C.M.A. Brick – “Specification of the design and construction” Of B.I.O.A.

III. STRUCTURAL SYSTEM

Per the original structural drawings, the primary building structural framing system and identified deficiencies are described below. 1. Basement

The building’s partial basement primarily includes the elevator equipment room, janitor rooms, mechanical room, trash room, storage rooms, electrical and fire pump rooms. The basement was built with two different structural wall types:

Concrete retaining wall at basement retaining area. The basement’s 12” concrete retaining wall was designed to resist the lateral pressure from the adjacent earth.

Masonry wall at non-retaining areas. Masonry walls (12” and 16” thick) were provided at the rear of building where no retaining requirements are needed.

Basement Slab. The basement slab is a 5” concrete slab on grade with wire fabric mesh.

2. Above Grade Exterior Walls

All exterior walls above grade were constructed of 4” brick veneer and 8” CMU with a 2” air gap in between. All exterior steel columns and spandrel beams were encased in the exterior masonry walls.

3. First Floor Slab The first floor is partially built above the basement and includes:

4 ½” elevated slab over the basement with 2” deep wide rib metal deck spanned between steel support beams.

5” slab on grade for the rest of the first floor area.

4. Mezzanine Floor Slab 4 ½” elevated concrete slab with 2” deep wide rib metal deck over a composite steel

beam framing system.

5. Roof The roof includes various elevations and two different roofing systems:


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A high skewed roof above the adult reading room was constructed of 5” laminated wood deck over Glulam Arches.

The remaining areas were constructed of 1 ½” wide rib metal deck over steel beam and column framing.

IV. FINDINGS The following findings are based on visual observations and do not include any testings.

1. Foundation wall During the assessment no defects were observed along the foundation walls and they are deemed to be structurally sound and in acceptable condition.

2. Masonry wall above grade

a. Stress cracks at masonry enclosure wall at column Gb-4a: (Photos #7, 8 & 54) Brick veneer around column Gb-4a exhibited 2 rows of vertical stress cracks. Per structural column table, the size of Gb-4a is W8x31. The length of the column is approx. 15 feet. Since there is no other column to receive the roof beam at the other end, the lateral force from any earthquake or wind is indirectly transferred to the adjacent columns through the roof diaphragms. Due to the lower slender ratio of the column, some deflection has occurred and created two vertical rows of stress cracks at the surface of the adjacent brick veneer. Repointing the cracked joints and replacing the broken brick is essential to eliminate current or future water penetration problems.

b. Loose brick and mortar joints: (Photos #20 & 21) The issue stems from the spandrel beams at the roof or mezzanine floor. Per the waterproofing detail 4/A-10, a flexible tie secured to the steel beam web was used to bond the inner and outer masonry wythes together. In addition, one layer of waterproofing membrane sheet was installed between the two wythes. In order to avoid the waterproofing intrusion and penetration of the flexible anchor, it is possible that the anchor may have been eliminated during construction. Without strong anchoring to bond the two wythes in place, any accumulated moisture over the slippery membrane underneath the mortar joint are not allowing to retain the masonry in its proper position. Eventually any lateral wall movement caused loose bricks and mortar joints to appear on the wall surface. Further study of this problem by opening the problem area is needed. Modification of the waterproofing and reconnection of the flexible anchor to the steel beam web are also deemed essential.

c. Water stain walls: (Photos # 9, 17, 18, 19, 21, 22, 23, 24, 25, 26, 27, 28, 29, 35, 41, 42, 43, 44, 45, 46, 55, 56, 57, 58 & 60 ) Serious efflorescence was noted in the upper portion of the exterior building masonry wall and rear wing wall surfaces. We believe that in the mortar, the hydrated lime contained some soluble calcium hydroxide as a product of the reaction between lime and water. When this calcium hydroxide was brought to the surface by the water, it combined with carbon dioxide in the air to form calcium Carbonate (very slightly soluble), which then appeared as a whitish deposit. This water penetration was through the roof flashing or coping. The roof counter flashing was reportedly repaired two years ago and the coping was apparently reinstalled after the new counter flashing was in place. Unfortunately this work does not appear to have resolved the water penetration problem. Several surface hair cracks were observed on the cast stone coping. The cracks are potential water penetration sources.


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The coping detail shown on sheet A-10 indicates that the cast stone coping (with a metal counter flashing below it) was secured to the masonry wall below with steel dowel anchors at 4’-0” O.C. According to the field survey, the size of the coping is about 10”x4’-0”. It is possible that the spacing of the coping anchors could have been alternated during installation but there is no information to this effect in the referenced document. The roofing repair detail on sheet R-2 prepared by ECS LLC shows a similar detail but without anchorage between coping and the masonry parapet wall. It is therefore possible that water penetrates into the coping through surface cracks that became wider as a result of freeze and thaw action. The cracks represent the more vulnerable points that allow water to penetrate into the coping and flashing lapping joints. Since there is apparently no anchorage between the masonry wall and coping, the different ratio of shrinkage and contraction between metal counter flashing and the cast stone coping will make the bonding agent loose and will accelerate the coping’s deterioration. Reexamining how the existing coping and counter flashing are connected is essential. Replacing the cast stone coping or cladding it (less desirable due to its deteriorating conditions) with metal coping should be considered to remedy water infiltration.

d. Vertical wall separation joint at stair #1: (Photos # 11, 12, 14 &19) The reported crack in the front staircase wall adjacent to the main entrance is deemed to be a construction joint between two different types of wall. One part of the wall is over the basement and the other part is without basement. The separation joint between the two wall sections is structurally acceptable.

e. Wall control joint installed at wrong location: (Photo #9) A vertical wall control joint was found on the south side wall approximately 1’-4” from column C-1. The structural drawing indicates that there are two rows of 14”x16”bond beams with continuous 6-#5 welded to the steel column at each end. One is located at the second floor elevation. The other is located at the roof elevation. Since the bracing bond was apparently cut off during the installation of the wall control joint, a portion of the wall has shifted approximately ¼” at the top. The wall height is approximately 26’-8”. The wall was constructed of 4” brick veneer and 8” back up CMU with 2” air gap in between. There is no other bracing provided at the top and the wall acts as a free standing structural element. Monitoring the movement at the top of the joint is essential and rebuilding the bracing at the top of the wall is required.

3. Concrete slab

a. Separation crack: (Photo #13, 39 & 40 ) A visible crack was noted on the vinyl floor tile in the first floor work room. It is a natural separation joint between the existing slab on grade and the elevated framing slab. As a result of the concrete’s contraction action, the slab movement has already torn up the vinyl floor along the joint. Cosmetic leveling along the joint before installing new flooring will reasonably conceal the separation.

b. Moisture at floor:

(Photo # 1, 2, 3, 4, 5, 6, 15, 16, 55 & 59) A high moisture degree was noted along the floor of the front and north side of the lobby. Improper exterior grading was also noted near these areas. Since the property line is along the north building wall, it is not permissible to discharge surface water from the library onto


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the neighboring property through weep holes or drains. The resulting serious water ponding is the cause of the observed damp floor surfaces. In the original drawings, section 3/A-10 indicates that the entire north building wing wall along the property line is supported by cantilever steel cast into concrete. The original design shows an 8’-2” cantilever from the basement wall to the north building wall edge. At the cantilever the floor was constructed of 5” concrete slab on grade. Per soil test boring #2, silty sand was encountered in this area. The silt is easily transferable and it can be reasonably anticipated that the surface running water will eventually undermine the sub-base of the concrete slab and cause further slab settlement. The high moisture underneath the slab together with freezing and thawing action will move the ground and slab up and down. No serious settlement was noted at the slab but user reports and friction marks visible on the entrance door framing indicate that when the ground swells there is some difficulty for the library front doors to open smoothly. Additionally if the steel beams cast into concrete are immersed into high moisture too long, it will cause the steel to corrode and affect the integrity of the beams. Since these steel beams support the entire north side wall along column line 6, the potential defect will create a serious safety hazard to the building. Therefore dewatering the ground adjacent to the building wall should be addressed immediately.

4. Roof

a. Blisters (Photos #30, 31,32,33,34, 36, 57, 58, 59 & 60) A limited number of roof blisters were observed during the initial site visits (April-May) while the weather was dryer but multiple blisters—small (4”x8”) to large (24” x 36”)—were observed during the last two inspections when ambient humidity was much higher. Blister are usually caused by air or moisture trapped between ply of roof membrane (or between rigid insulation and membrane). The moisture is either from water leaking under the membrane or from high moisture that was previously trapped in the existing roof and was not removed completely prior to installation of the new roofing. Any crater resulting from perforated blisters allow additional moisture penetration that can further weaken the roof. The blisters also cause the decline of adhesion of tar. Loose adhesion and blisters make the roof more vulnerable to water penetration problems. Based on ECS’s roof repair plans and specifications dated 5/25/2011, the work was primarily limited to flashing repairs around the parapet wall and some adjacent areas. The reviewed documents did not include instructions to remove all damaged roof or wet material underneath the roofing. It is our view that the previous repairs did not result in a permanent remedy. The proper removal of the trapped moisture together with the recommended coping remedial work should be implemented as part of a major roofing overhaul.

b. Improper step flashing at skew roof & cast stone coping at parapet wall

Upon examination of the skewed roof above the corroded mezzanine steel beam (see next section) it appeared that the step flashing was installed improperly. Step flashing is usually secured to the roof sheathing directly before the waterproofing membrane is applied. Observed conditions however show that the step flashing was instead installed on top of the roof shingles then covered with asphalt roofing felt and shingle. If the shingle deteriorates, or melting snow accumulates, the step flashing will not function as intended and will cause water leaks.


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Successive repairs were apparently made is this area including reinstalling the counter flashing on the other side of the wall (along the flat roof) and repeated caulking of loose joins. Heavy but loose caulk was used under the coping to fill the void between the coping and top of masonry parapet wall. None of these repairs have since resolved the water penetration problems.

5.Structural framing

a. Corroded steel beam at Mezzanine roof (Photos 37, 38, 43, 44, 46, 47, 48, 49, 50 & 51) The reported corrosion problem at the steel beam located at column C-1 is the result of water leaking from the roof. The survey showed that during the initial construction one piece of roof deck was not extended far enough to reach the top of the steel beam and was stopped about 1” shorter from the face of the steel beam flange. It appears that one small make up piece of deck was therefore welded to the top of the steel beam to connect it to the shortened deck. Since there is no rigid support at one end of the deck, it has created a flexible spliced deck joint which is vulnerable to water penetration as confirmed by surface water stains on the adjacent west wall. Installing an additional support for the non-supported roof deck and correctly reinstalling the step flashing at the skewed roof are essential to eliminate leakage in this area. Removing the corrosion around the corroded steel beam and repainting the steel surface with antirust coating is necessary to prevent further steel damage.

b. Corroded steel supporting steel system for roof top units. ( photo 52 )

The existing steel beams and stools were observed to be consistently rusted and in need of immediate attention. The corroded surfaces must be steel brushed clean and rustproofing paint must be applied to avoid further corrosion that can affect the integrity of the steel.

V. RECOMMENDATIONS 1. Masonry wall above grade

a. Stress cracks at masonry enclosure wall at column Gb-4a Repoint the cracked mortar joints and replace the broken brick.

b. Loose brick and mortar along the floor and roof steel spandrel beams.

Open and examine the defect area to determine the source of problem. Modify the waterproofing and resecure the flexible anchor to the steel beam as necessary.

c. Water stain exhibited at surface of wall

As indicated the major source of water leakage is apparently from the cast stone coping. Replace or clad (less desirable) the existing coping with metal coping over 2- 2x10 treated nailers secured to top of existing masonry parapet wall with ½”x0’-6” expansion bolts set @4’-0” O.C. with waterproof gaskets.

d. Vertical separation joint at wall of stair #1

Remove the regular cement mortar at joint and replace with flexible joint seal set into the separation joint.

e. Wall control joint installed at wrong location.

Monitor the movement of top of wall. Provide 2 rows of wall bracing beams between laminated columns in order to brace the wall at top and middle of wall.


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2. Concrete Slab

a. Floor separation crack at work room No structural remedy work is needed. Use floor leveler to conceal defect.

b. Moisture at entrance floor

Dewater area by modifying grade and consider reaching agreement with neighbor to. run a drainage pipe along the north wall and tie into the rear yard storm sewer. Alternatively consider the feasibility of using an interior sum pump to drain the excess water into the sewer system.

3. Roof

a. Blisters Option 1: Identify and mark all visible blisters during suitable conditions. Subsequently await dry weather conditions to remove roofing and wet insulation around blisters and extend work to encompass all damp roof areas completely and allow exposed roof deck to dry. Once the deck is dry, install new insulation and roof membrane immediately.

Option 2: Fully remove all roofing and insulation material down to deck. Allow to dry and install new insulation and roof membrane.

b. Improper step flashing at skew roof

Remove and replace step flashing and also replace roofing felt and shingle as required.

4. Structural framing

a. Corroded steel beam under Mezzanine roof Provide a shelf angle welded to existing steel beam to receive the existing spliced deck, fix the step flashing at slopping roof above and replace the cast stone coping with metal coping in order to fix water leaks in this area. Brush the surface of corroded steel and coat it with antirust paint to avoid further future damage.

b. Corroded steel supporting roof top units

Perform the same procedure as above.

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11/18/14

FOLLOW-UP EVALUATION

ADDITIONAL ROOF SURVEY

I. Roof Leaks An additional waterproofing survey of the Shepherd Park Library roof was conducted on Monday 11/17/14 following heavy overnight and morning rains. Visible water streaks were observed below the mezzanine’s south ceiling corner in the vicinity of were previous water marks were noted. The water appeared to be dripping along the face of the masonry wall and was visibly coming from a higher ceiling location than previously observed.


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Additional water infiltration not previously observed was also noted at the top of the roof access stairway. The water seepage location implies that the water was coming from the small roof area above the stairway. A more detailed check of the upper roof could not be made at the time the survey was conducted.

II. Roof Conditions The built-in copper gutter and scupper located above the interior mezzanine wall drips were checked and did not show any additional open cracks or seams. The visible conditions suggest that the leak may be emanating from defective flashing and/or from the higher skewed roof that drains over the copper gutter. Additional water testing should be done in that area as soon as conditions permit.


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During this assessment the ambient temperature was in the low 30s and most of the roof membrane blisters previously documented during much warmer and more humid summer conditions were not visible. Some of the previously documented large roof membrane blisters were however highly noticeable and their surface showed stress marks that appeared bristle. It is likely that the stretched membrane over these areas will continue to deteriorate at an accelerated pace.

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11/26/14

FINAL SURVEY

ROOF SURVEY

I. Traced Leaks A final waterproofing survey of the Shepherd Park Library roof was conducted on Wednesday 11/26/14 during snow and rain conditions. The water streaks previously observed and noted in the 11/18/14 report were noticeably more visible below the mezzanine’s south ceiling corner. The water was clearly dripping along the face of the masonry wall and was visibly coming from the same ceiling location previously observed. An additional assessment of the roof area immediately above the leak showed open seams in an existing copper patch repair.


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The additional water infiltration previously observed at the top of the roof access stairway was also noticeably dripping during this assessment. Additional checking of the roof above the stairway indicated open roofing seams around the drain scupper.

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