Amend 4_Structural Slab Testing PWS Rev QA Amend.pdf

Performance Work Statement Structural Tests of Slab-Column and Slab-Beam-Column Connections for the Champlain Towers South

A. Background

The National Construction Safety Team Act (“Act”), Pub. L. 107-231, codified at 15 U.S.C.

7301 et seq., was enacted to provide for the establishment of investigative teams (“Teams”) to assess building performance and emergency response and evacuation procedures in the wake of any building failure that has resulted in substantial loss of life or that posed significant potential for substantial loss of life. The purpose of investigations by Teams is to improve the safety and structural integrity of buildings in the United States. As stated in the statute, a Team shall (1) establish the likely technical cause or causes of the building failure; (2) evaluate the technical aspects of evacuation and emergency response procedures; (3) recommend, as necessary, specific improvements to building standards, codes, and practices based on the findings made pursuant to (1) and (2); and (4) recommend any research and other appropriate actions needed to improve the structural safety of buildings, and improve evacuation and emergency response procedures, based on the findings of the investigation. In addition, the National Institute of Standards and Technology (NIST) has promulgated regulations implementing the Act. The regulations are found at 15 CFR part 270.

On June 24, 2021, the Champlain Towers South (CTS) Condominium in Surfside, Florida, collapsed after nearly 40 years of service. Ninety-eight people died in the collapse and several others were injured. NIST sent a preliminary reconnaissance team to collect information and data related to the collapse. Based on the recommendations of the preliminary reconnaissance team and evaluation of the criteria listed in the regulations implementing the Act, specifically in 15 CFR § 270.102, on June 30, 2021, the Director of the National Institute of Standards and Technology (NIST), United States Department of Commerce, established a Team to study the collapse of the CTS Condominium in Surfside, FL. The NIST Investigation comprises six projects; including the Structural Engineering project whose focus is to determine (1) the technical conditions that led to the collapse of the Champlain Towers South and (2) the factors that might have contributed to the collapse including building design, construction, maintenance, and materials based on sophisticated structural models that make use of (a) evidence collected from the collapse site, (b) results of the other Investigation projects, and (c) structural engineering and reinforced concrete design and mechanics knowledge.

NIST requires support services to conduct laboratory testing on full-scale reinforced concrete components representative of collapsed portions of the CTS building. Appendix A of this document shows some representative drawings from the structural drawing set of the building released by the city of Surfside, Florida. Figure A.1 shows the structural drawing for the Lobby Level Framing Plan, which includes the first-floor level within the footprint of the multi-story tower plus the plaza (or pool deck) slab to the south and east of the tower. The region of interest for the required services is the region bounded in the east-west direction by grid lines J and Q, and in the north-south direction by grid lines 8 and 15 (inside the blue outline in Figure A.1). This area was designed as a flat-plate construction with specified slab thickness of 9-1/2 in. Typical bottom reinforcement in the slab was specified to be No. 4 bars at 12 in on center each way and typical top reinforcement at slab-column connections was specified to be No. 5 bars with center-to-center spacing generally in the range of 6.0 to 7.5 in. In the plaza area to the south of the tower (south of grid line 9.1), the flat plate was supported by single-story columns of size 12 in x 16 in with four No. 7 longitudinal bars that were bent outward into the slab (Figure A.2(a)). Along the south edge of the tower, between grid lines 9.1 and 11.1, a series of steps in the slab elevation transitioned from the lobby level downward to the plaza level, resulting in slab drop “beams” and Beams Type A (Figure A.2(c and d)). All reinforcement was specified as ASTM A615 Grade 60. Within the region of interest, two different concrete strengths were specified (fc’ = 4000 psi for floor concrete and fc’ = 6000 psi for column concrete).

B. Purpose and Objectives

NIST requires support services to conduct a laboratory test project to construct, instrument, test, and prepare reports on strength, deformability, and failure modes of slab-column connections with and without the slab drops and Beams Type A described above. The required services are in support of the NIST’s investigation into the CTS building collapse.

Specifically, the objectives of the required services are to:

1. Determine the strength, deformability, and failure modes of eight plus one optional representative slab-column connections from the plaza level south of grid line 9.1, some with uncorroded reinforcement and others with corroded reinforcement, and obtain data that can be used to support numerical simulations of the behavior of the building.

2. Determine the strength, deformability, and failure modes of two representative slab-column connections along grid line 9.1, including effects of slab drops, Beams Type A, column offset bent reinforcement, and prior failure of the plaza slab south of and adjacent to grid line 9.1, with uncorroded reinforcement, and obtain data that can be used to support numerical simulations of the behavior of the building.

C. Scope

The Contractor shall develop and deliver all labor, material, equipment, project oversight, report writing, administration, and technical execution necessary to meet the stated requirements and conduct the work described in the tasks below, with the exception that NIST will provide the concrete mixture designs and the concrete aggregate, cement, and any admixtures required to make the concrete used in the test specimens and concrete test cylinders. The Contractor shall be responsible to transport the coarse and fine aggregates, cement, and any admixtures from a location in Miami, Florida to the Contractor’s testing laboratory (see Appendix B). The Contractor is responsible for all other materials. As stated in section B, the scope includes eight base requirement slab-column test specimens, plus one optional requirement slab-column test specimen, and two base requirement slab-beam-column test specimens.

D. Tasks

The project requirements include two experimental tasks: Task 1 to test slab-column connections representative of those in the pool deck and Task 2 to test slab-beam-column connections representative of those along grid line 9.1. The two tasks (a) need different experimental apparatuses and setup and (b) shall be conducted simultaneously. The Contractor is encouraged to conduct the two tasks in two different structural testing laboratories, possibly with different administering entities, to maximize project schedule efficiency.

Task 1: Tests to Investigate Strength, Deformability, and Post-failure Behavior of Slab- Column Connections

Overview and Description of the Test Program

Overview

This task requires the Contractor to design, acquire materials, construct, instrument, test, and report results from tests on slab-column connections representative of those that existed in the plaza area of the CTS building south of grid line 9.1 highlighted in Figure A.1. The tests shall establish strength, deformability, and failure modes of connections to provide an insight into the behavior and failure mode(s) of the connections and to support NIST numerical models of the CTS building.

The plaza area (Figure A.1) of the CTS building consists of a 9-1/2-in. thick, conventionally reinforced slab supported on single-story columns having 16-in. by 12-in cross section. The columns are reinforced with four No. 7 longitudinal bars that are bent outward into the slab (Figure A.2(a)). Although testing under Task 1 shall emphasize behavior under vertical shear without moment, at least two tests shall include a test apparatus capable of imparting both vertical shear and moment transfer between the slab and the column. For these two tests, the combination of shear and moment transfer will cause some rotation of the column, which is to be permitted. To help understand possible effects of reinforcement corrosion, testing both with and without reinforcement corrosion are required in Task 1. Finally, while most of the plaza slab-column connections involve a slab of constant thickness, some slabs are stiffened by Beams Type A (Figure A.2(c)), and one test in Task 1 shall include this beam. Beam Type A has a width of 12 in and an overall depth of 15 in (9.5 in slab depth + 5.5 in projection below the slab). For this test, the asymmetry of the slab will tend to cause some column rotation, but the test apparatus will need to be capable of maintaining the column in a vertical (plumb) position without significant rotation or lateral translation.

Schematic Test Apparatus

NIST anticipates that the slab-column tests shall be conducted using an apparatus similar to the one shown schematically in Figure 1.1, which is based on Guandalini et al. (2009).

Alternative testing methods achieving loading conditions on the connection may be proposed for consideration by NIST. Alternative apparatus shall approximately reproduce the nearly axi-symmetric shear and moment distributions, as well as shear to moment ratios in the slab near the column as are produced by the apparatus shown in Figure 1.1. In the schematic shown, a centrally located column is loaded vertically upward with force V using a hydraulic jack while the slab is supported at eight pinned support points located at equal-length arcs around a circle of radius r. For symmetric slab geometries under direct shear without moment on the column, the slab supports may be rollers and the column load may be applied without need to restrain the system from horizontal movement. Some of the specified tests, however, involve a slab geometry that is not symmetric in plan such that restraints against horizontal displacement of the slab and column are needed. See specific test descriptions for additional details.

As shown in Figure 1.1, the slab has a thickness h = 9-1/2 in. to match the thickness of the plaza slab. The column cross section is 16 in by 12 in, as specified in the drawings for columns supporting the plaza slab. The circle of radius r for these tests shall have a typical value of r = 5 ft, but two test specimens shall have values of r as small as 3 ft. NIST will consider proposals to modify the value of r by +/-4 where that modification will result in appreciable cost savings for the test apparatus. Additionally, while most of the tests required shall apply vertical shear V without moment, the Contractor should anticipate two tests with both shear V and moment Msc transferred between the slab and column slab-column connection. The slab will necessarily extend horizontally beyond the dimension r as required to develop reinforcement and avoid local failures of the slab, but this extension shall not exceed 6 in at the narrowest points, so as to avoid excessive constraint from the overhanging slab segments. The actual extent of the slab beyond the dimension r is to be determined by the Contractor, subject to the constraint noted above.

Each test specimen includes both (a) a column stub extending below the slab and (b) the slab (plus Beam Type A in one test specimen). NIST is specifying the dimension r of the slab and the cross-sectional dimensions of the column. The length of the column extending below the slab is to be selected by the Contractor but shall be at least 32 in and not more than 106.5 in.

Figure 1.1 – Schematic of slab-column connection test specimens. Note: Penetrations through the slab at the loading/reaction plates are permitted. Otherwise, slab penetrations are not permitted.

Test Matrix

The Contractor shall plan for a total of eight full-scale slab-column tests as part of base requirements. One additional optional full-scale slab-column test may also be required at Government discretion as described later in this Performance Work Statement. The full-scale slab-column tests shall have overall configurations, loadings, and descriptions as summarized in Table 1.1 below. Additional test specimen details are provided later in this document. NIST reserves the right to make minor changes to the test matrix and to individual test specimens but agrees that any such changes will not materially increase specimen sizes, complicate the configurations, or affect reinforcement acquisitions quantities or details.

Table 1.1 – Slab-column test specimen test matrix*

Test specimen designation

Group1 Radius r (ft)2

Corrosion3 Column Hooks4

Beam Type A5

Moment6

SC-A1 A 5 0 Out No No SC-A2 A 5 1 Out No No SC-A3 A 3 0 Out No No SC-A4 A 3 1 Out No No SC-B1 B 5 2 Out No No SC-B2 B 5 0 Out Yes Yes/No SC-B3 B 5 0 Out No Yes SC-B4 B 5 2 Out No Yes

OPTIONAL

SC-B5

B 5 0 In No No

1It is anticipated that the test specimens will be constructed in two groups of four or five specimens each, designated Groups A and B. Other options may be proposed for consideration by NIST.

2See Figure 1.1 for definition of the radius r.

3Three test specimens shall undergo accelerated corrosion prior to completing the structural tests. Degree 0 indicates no corrosion. Degrees 1 and 2 designate two different degrees of accelerated corrosion. NIST will specify the degrees of corrosion, measured by percentage loss of reinforcement mass within the slab, at a later date prior to the corrosion protocol.

4Column longitudinal reinforcement hooks were bent Out into the slab in the pool deck of the CTS. One optional test specimen (SC-B5) shall have the bars bent In.

5Specimen SC-B2 shall have a Beam Type A.

6All specimens shall have concentrically applied vertical load on the column except Specimens SC-B3 and SC-B4. Note that Specimen SC-B2 with Beam Type A will tend to develop joint rotations under vertically applied load such that some column rotational/translational restraint shall be required, which will also induce column moment.

Materials, Construction, and Materials Testing

Under a project distinct from this requirement, NIST is studying reinforcement and concrete constituent properties and mechanical properties. NIST will use the results of its studies to specify materials, proportions, and methods for making different concretes for the slab and columns with material properties approximating those in the original CTS building.

Additionally, NIST will source, store in a location in Miami and make available, free of charge, the coarse and fine aggregates, cement, and any admixtures required for making concrete for the specimens of Task 1 of this Performance Work Statement (see Appendix B). The Contractor shall (1) transport the aggregates and cement from Miami to the Contractor’s testing laboratory, (2) make a test batch of the concrete for Task 1 following the procedures provided by NIST, and (3) make the concrete for Task 1 following the procedures to be provided by NIST. Procedures will be provided prior to concrete mixing and casting.

Prior to transporting aggregates, cements, and admixtures, the Contractor shall provide for NIST review and approval a safety plan for loading materials into the trucks in the Miami location identifying potential hazards and procedures for mitigating such hazards. The plan shall include safety controls, Personal Protective Equipment (PPE) required and to be provided by the Contractor, what training has been provided to Contractor employees, and an emergency response plan. The plan shall be submitted electronically via email to the Contracting Officer’s Representative (COR).

The test batch of the concrete described in the previous paragraph is to give the Contractor experience with batching and mixing the specified concrete mixture for the “Nominal 4000-psi Floor Concrete” and to verify that the mixture produces the intended slump and hardened mechanical properties. NIST intends for the slump to be in the range of 4-6 in. NIST intends for the 28-day compressive strength to be in the range of 3000 to 5000 psi. The target compressive strength range may be changed by NIST at a later date via bilateral modification.

The concrete for casting the test specimens shall be mixed using a large-capacity mixer with carefully weighed ingredients added at the Contractor’s lab or alternatively shall be provided by a ready-mix contractor who has been instructed by the Contractor in the objectives of achieving a target concrete compressive strength and the importance of achieving the specified mixture proportions. NIST advises that good batching practice is to hold out a specified amount of water from the mixer, sample the mixture for slump, and then adjust water and admixtures with the intent of achieving both the target slump and target compressive strength. The Contractor shall convene a meeting with NIST in advance to describe the approach to be used in mixing and placing the concrete, subject to NIST’s approval.

The Contractor shall also provide and fabricate steel reinforcement for the Task 1 specimens.

Construction of reinforced concrete test specimens shall be done in accordance with generally accepted good construction practices, such as those identified in ACI 301-20 (2020).

All steel reinforcement shall be ASTM A615 Grade 60 reinforcement with actual yield strength in the range 60 to 77 ksi. Coupon tensile strength testing of representative reinforcing bars of all sizes shall be conducted in accordance with ASTM A370-21 (2021) to determine engineering stress-strain relationships. At least three tests shall be reported per bar size.

Tests shall be conducted on full-section specimens, rather than machined specimens, with stress calculated based on nominal cross-sectional area.

As noted previously, each slab-column test specimen comprises (a) a column stub extending below the slab and (b) the slab (plus Beam Type A in specimen SC-B2). For each specimen, the column stub is to be cast first using the concrete mixture design to be specified by NIST for “Nominal 6000-psi Column Concrete.” Column concrete shall be allowed to harden before placing slab concrete. Before placing slab concrete, any laitance or standing water at the top of the column concrete shall be removed, but the surface shall not be otherwise roughened.

The slab (plus Beam Type A in specimen SC-B2) shall be cast using the concrete mixture design specified by NIST for “Nominal 4000-psi Floor Concrete.” Test specimens are to be cast in an upright position such that the effects of casting direction, if any, are properly reflected in the results.

Test specimens shall be wet cured for 7-14 days, or as otherwise required to best achieve target compressive strengths at time of final testing. After wet curing, test specimens may be removed from their wet-curing environment to prepare them for testing.

For each batch of concrete used in the test specimens of Task 1, the Contractor shall make a sufficient number of 6 in by 12 in concrete cylinders in accordance with ASTM C 192-02 (2002) to be used for monitoring the development of concrete material properties. At least three cylinders shall be tested for compressive strength (in accordance with ASTM C39-21 (2021)) at each of 7 days, 14 days, 21 days, and 28 days. At or near the date of final testing of a slab-column test specimen, three additional cylinders shall be tested in compression in accordance with ASTM C39 and ASTM C469-14 (2014) to obtain compressive strength, Young’s modulus, and the complete compressive stress-compressive strain relationship up to the peak stress capacity, plus three additional cylinders shall be tested for splitting tensile strength in accordance with ASTM C496-17 (2017). Cylinders shall be cured along with and under nominally identical conditions as the test specimens rather than being cured in a fog room. The objective of the cylinder tests is to be able to monitor the development of the concrete strengths over the duration of the test specimen tests and to obtain more complete information about mechanical properties on the final day of testing of a test specimen.

Within one week after completion of structural testing on a slab-column test specimen, one 4-in diameter, vertically oriented core shall be obtained from a visibly representative undamaged portion of each test slab. The core shall be located to avoid coring through slab reinforcement.

The core specimen shall be tested in compression in accordance with ASTM C42-20 no later than one week after removal from the test slab.

For all test specimens, the Contractor shall obtain ultrasonic pulse velocity (UPV) measurements for concrete in accordance with ASTM C597-16 (a) at four distinct locations within each test slab, including two locations within 18 in from the face of the column on the day of and prior to testing, (b) for the three concrete cylinders to be tested in compression at or near the final testing date of each slab-column test specimen, and (c) for the core removed from each slab-column test specimen after final structural testing of the slab-column test specimen. The objectives of these UPV measurements are to (1) develop a concrete mixture-specific correlation between UPV test results and compressive strength from cylinders and cores; (2) identify internal voids or discontinuities in the specimens that could influence test results; and (3) make inferences about the in-place strength of the concrete in the test specimens based on the correlation developed among cylinder and core strength, and pulse velocity. For cylinders and cores, pulse velocity shall be obtained immediately prior to compression testing, and in the moisture condition that pertains during compression testing.

For the test specimens, pulse velocity shall be obtained prior to initial structural loading, but no sooner than 14 days after casting, and at least 7 days after removing curing covers to allow uniform drying of all surfaces. See ASTM C597 for notes concerning the influence of degree of saturation and acoustic coupling between the transducers and the concrete surface. The Contractor shall determine optimum coupling method prior to testing to ensure that the same coupling technique is used for all tests. The Contractor shall perform automatic zero-time adjustment or shall use a reference bar to calibrate the instrument. For all UPV measurements, the Contractor shall place transducers directly opposite each other with a straight, uninterrupted wave travel path. It is expected that embedded reinforcing steel will influence results. At each designated measurement location, the Contractor shall obtain at least three (3) individual UPV measurements, in each case pressing the faces of the transducers firmly against the surfaces of the concrete until a stable transit time is displayed.

The Contractor shall report the results in accordance with ASTM C597-16.

In addition, for corroded specimens SC-A2, SC-A4, SC-B1, and SC-B4 the Contractor shall obtain UPV measurements throughout the duration of the corrosion protocol. These UPV measurements shall cover the entire area of the slab where corrosion damage is anticipated and shall define the extent of internal damage including delamination. Additionally, displacement transducers shall measure the thickness and change of thickness of the slab during the duration of the corrosion protocol. The measurements shall be taken at least at two locations a distance equal to 8 in from the column face on opposite sides of the column. For the latter measurements, the Contractor shall create a small penetration through the slab thickness by drilling through the slab after casting or preferably by installing some weak elements prior to casting that provide a narrow penetration through the slab or that can be drilled out to create a narrow penetration. A wire passing through the penetration shall then be attached to a displacement transducer to measure any changes in thickness.

Instrumentation, Testing, and Data Recording

Instrumentation shall include the following at a minimum:

Shear force transferred between the slab and column, based on measurements using one or more force transducers. Reported values shall be adjusted to account for specimen self-weight.

Vertical reactions at each of the supports, plus displacements at the same locations if the supports are flexible or move as part of the loading system.

Vertical displacements at the top and bottom of the slab and slab rotations relative to horizontal, measured at small intervals along both principal axes. Measurements shall be sufficient to define the displacement field of the slab relative to the column.

Measurements at the bottom and top surface of the slab are required so that vertical dilation of the slab associated with formation of inclined cracks in the slab can be identified. See Guandalini et al. (2009) for example instrumentation.

For tests without accelerated corrosion, electrical resistance strain gauges attached to slab top and bottom reinforcement and to column hooked bars at intervals sufficient to determine variations of strains within the slab.

Digital photography to identify cracking and failure patterns, as well as digital videos with high-quality lighting to record the tests including occurrence of failure.

The Contractor shall identify slab shear failures as a function of (a) the shear force on the slab critical section and (b) the angle ψ between the slab over the column and the slab outside the critical section (Figure 1.2). Measurement of relative vertical displacements along lines ab and ac (Figure 1.2) shall be used to derive this information. See Guandalini et al. (2009) for additional information on the rotation ψ.

Data acquisition systems shall provide for effectively continuous data sampling throughout important stages of testing.

The Contractor shall use equipment that is maintained and calibrated in accordance with accepted good practices, including those following in this paragraph. Unless otherwise approved by NIST, the data acquisition system shall be calibrated by an external ISO-17025 accredited lab approximately once every two years; force-measuring instruments and systems shall be calibrated at intervals not exceeding two years in accordance with ASTM E74-18e1;

and position transducers shall be calibrated using the procedures and at intervals as specified in ASTM F2537-06(2017)by using high-precision calibration blocks that are certified by an ISO-17025 accredited lab of the manufacturer. Equivalent or better calibration practices shall be considered. For all measurements, the Contractor shall furnish to NIST the calibration records or methods of the instrumentation used and shall report the precision in the measurement.

Figure 1.2 – Minimum required instrumentation (partial), showing lines ab and ac along which vertical relative displacements are to be measured.

NIST requires reporting of uncertainties associated with measured/reported data and, when applicable, analyses of those data. The Contractor shall quantify and report uncertainties of any data or analyses of data associated with the approaches/methodologies used in this requirement. The procedures for evaluating uncertainty shall be reported in accordance with the guidance found in NIST Technical Note 1297 (Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results).

Upon completion of all tests described for this task, the Contractor shall submit to NIST the raw/native and processed digital data (with uncertainty estimates) including loads, reactions, displacements, strains, and rotations, along with digital photographs and videos. NIST will set up a Box folder for the Contractor to upload the data.

Simulated gravity load tests shall be conducted using a quasi-static loading by slowly applying vertical displacement of the column (or equivalent alternative displacement consistent with the test apparatus). The Loading rate shall be sufficiently slow to allow for the full development of slab cracking with minimal dynamic effect. Testing shall continue through the onset of slab failure and until the full failure configuration is visible and vertical load has dropped to a fraction (less than about 10 %) of maximum capacity and the column is fully punched through the slab to expose the final geometry of the failure surface. Unloading and shimming or resetting the loading apparatus after initial failure is permitted to achieve this final failure condition. It is acceptable to remove some instrumentation after failure initiation such that instrumentation damage is minimized. Note that testing of corroded specimens SC-A2, SC-A4, SC-B1 and SC-B4 will deviate from this simulated gravity loading protocol because of requirements for preloading, followed by an accelerated corrosion protocol, and then final continued simulated gravity loading until failure. See the detailed testing description for Specimens SC-A2, SC-A4, SC-B1 and SC-B4 later in this document.

The Contractor shall conduct the tests with the degree of skill and care that is required by current, good and sound laboratory test procedures and practices prevailing at the time the services are performed. The Contractor shall use video cameras and/or stationary cameras taking high-resolution photographs at fixed intervals to provide a continuous record of the tests and shall supplement these records with detailed photographs at key points of testing. The Contractor shall also mark crack locations and measure crack widths using a crack comparator. The Contractor shall keep a detailed written test log for each test.

Construction Details of the Test Specimens

Details of Specimen SC-A1

Figure 1.3 shows details of the slab-column connection for Specimen SC-A1. Top reinforcement comprises No. 5 bars at 7 in on centers each way. Bottom reinforcement comprises No. 4 bars at 12 in on centers each way, with bars centered on the column and alternate bars lap-spliced along a length of 6 in centered on the column axis. The outer layers of slab top and bottom reinforcement are oriented perpendicular to the 16-in dimension of the column. Clear cover for the outer layer of slab bottom reinforcement is ¾ in. Effective depth measured from the bottom of the slab to the centroid of the top slab reinforcement (the intersection between the outer and inner top reinforcement layers) is 7.75 in. This effective depth is an approximate value that NIST will specify at a later date. The slab is supported by a column having gross cross-sectional dimensions of 16 in by 12 in. Column longitudinal reinforcement comprises four No. 7 bars, one located in each corner of the column, supported by No. 3 ties at 3 in on centers. The No. 7 bars are bent to form a standard hook that extends outward into the slab at mid-depth, with the extension on the hooks parallel to the 16-in column dimension. The specified dimensions and details are critical to the required test. The height of the column is not critical to the test. As noted elsewhere, the minimum required extension of the column below the slab is 32 in while the maximum dimension is 106.5 in.

Note the position of the construction joint in Figure 1.3. As noted elsewhere in this document, column concrete shall be allowed to harden before placing slab concrete. Before placing slab concrete, any laitance or standing water at the top of the column concrete shall be removed but the surface shall not be otherwise roughened.

Figure 1.3 – Elevation of slab-column connection for Specimen SC-A1.

Figure 1.4 shows the overall slab reinforcement arrangement, in which the slab reinforcement extends to near the edge of the slab with allowance for reasonable concrete cover.

Not shown in these figures, Specimen SC-A1 is expected to have a value of r = 5 ft. See Figure 1.1 for a definition of the variable r. NIST reserves the right to change the dimensions of r prior to specimen installation, but in no case will the specified dimension of r exceed 5 ft.

Figure 1.4 – Overall slab reinforcement arrangement.

N.B. heads instead of hooks are permitted as long as the heads satisfy ASTM A 970 or better.

Details of Specimen SC-A2

Specimen SC-A2 has identical gross dimensions and reinforcement as Specimen SC-A1.

Specimen SC-A2 shall undergo a different loading protocol that includes accelerated corrosion of the slab and column reinforcement. The specimen shall initially be subjected to the same simulated gravity loading protocol as Specimen SC-A1, except that loading shall stop at a fraction of the strength measured for Specimen SC-A1. This fraction is expected to be ¾, but NIST reserves the right to specify a different fraction at a later date prior to gravity load testing.

This simulated gravity loading is expected to result in significant cracking of the slab concrete and possibly yielding of the slab reinforcement. After unloading, the specimens shall be subjected to accelerated corrosion protocol to achieve target degree of corrosion, where degree of corrosion is defined as the ratio of loss of steel reinforcement mass after corrosion divided by the original mass. The degree of corrosion is expected to be 3 % for Specimen SC- A2, although NIST reserves the right to modify this value at a later date prior to the corrosion protocol. Accelerated corrosion shall be achieved through a salt pond created over the damaged slab or impressed electrical current, or a combination of the two. NIST expects to engage a corrosion expert under a separate contract to develop and demonstrate the accelerated corrosion protocol. That corrosion contractor, retained by NIST, will then work with the Contractor for this project, through the NIST Contracting Officer’s Representative (COR), to advise on the corrosion protocol and view its implementation. After completing the corrosion protocol, the gravity loading protocol shall be repeated for Specimens SC-A2, with loading continuing until failure of the slab-column connection.

Details of Specimens SC-A3 and SC-A4

Specimens SC-A3 and SC-A4 shall have dimensions and reinforcement identical to Specimens SC-A1 and SC-A2, with the exception that the value of the radius for SC-A3 and SC-A4 is r = 3 ft and the overall dimensions of the slab are reduced to avoid excessive overhanging slab segments, as described elsewhere in this document. NIST reserves the right to modify the radius between 3 ft and 5 ft at a later time.

The loading protocol for Specimen SC-A3 shall be identical to the loading protocol for Specimen SC-A1, that is, structural loading to failure without a corrosion protocol. The loading protocol for Specimen SC-A4 shall be similar to the loading protocol for Specimen SC-A2, that is, structural loading to a fraction of the strength measured for SC-A3 (that fraction being approximately ¾, but NIST reserves the right to specify a different fraction at a later date), followed by an accelerated corrosion protocol to achieve target degree of corrosion the same as that for Specimen SC-A2, followed by the gravity loading protocol with loading continuing until failure of the slab-column connection.

Details of Specimen SC-B1

Specimen SC-B1 shall have dimensions and reinforcement identical to Specimen SC-A1.

Similar to Specimen SC-A2, this specimen shall be subjected to preloading to a fraction of its capacity, followed by an accelerated corrosion protocol, followed by the gravity loading protocol until failure of the slab-column connection. The degree of corrosion for the accelerated corrosion protocol will be determined following review of the test results for Specimens SC-A2 and SC-A4.

Details of Specimen SC-B2

Specimen SC-B2 shall have dimensions and reinforcement identical to Specimen SC-A1 except a Beam Type A shall be incorporated in the slab on one side of the column. Figure 1.5 shows the details near the slab-beam-column connection. Note the position of the construction joint, which is positioned vertically at the same elevation as the bottom of the beam. Figure 1.6 shows the orientation of the Beam Type A in the schematic test configuration. Figure A.2(c) shows a conceptual cross section of Beam Type A.

The testing protocol shall be nominally the same as for SC-A-1. The presence of the Beam Type A on one side of the column introduces an asymmetry that likely will result in asymmetric displacement patterns. For this test, the column shall be restrained so that it undergoes essentially vertical translation without rotation. Where a short column stub is used, it may be acceptable to achieve this condition by preventing horizontal translation at the far (lower) end of the column stub.

Figure 1.5 – Elevation of slab-beam-column connection for Specimen SC-B2.

Figure 1.6 – Schematic of slab-beam-column connection test specimen SC-B2.

Details of Specimen SC-B3

Specimen SC-B3 shall have dimensions and reinforcement identical to Specimen SC-A1. The main difference is that the simulated gravity loading protocol includes transfer moment Msc in the direction of long plan dimension of the column (that is, moment vector perpendicular to the long plan dimension of the column) in addition to the applied shear. Placing V eccentric to the center of the column cross section is an acceptable method for applying the combined shear and moment. For planning purposes, the Contractor should estimate that the moment to shear ratio is Msc/V = 12 in. NIST reserves the right to modify this ratio at a later date.

Details of Specimen SC-B4

Specimen SC-B3 shall have dimensions and reinforcement identical to those of Specimen SC- A1. Similar to Specimen SC-A2, this specimen shall be subjected to preloading to a fraction of its capacity, followed by an accelerated corrosion protocol, followed by the simulated gravity loading protocol until failure of the slab-column connection. The degree of corrosion for the accelerated corrosion protocol will be determined following review of the test results for

Similar to Specimen SC-B3, the simulated gravity loading protocol shall include transfer moment Msc in the direction of long plan dimension of the column (that is, moment vector perpendicular to the long plan dimension of the column) in addition to the applied shear.

Placing V eccentric to the center of the column cross section is an acceptable method for applying the combined shear and moment. For planning purposes, the Contractor should estimate that the moment to shear ratio is Msc/V = 12 in. NIST reserves the right to modify this ratio at a later date.

Details of OPTIONAL Specimen SC-B5

The following Optional Requirement may or may not be exercised at the sole discretion of the Government in accordance with FAR 52.217-7: Option for Increased Quantity – Separately Priced Line Item. The option may be exercised at time of base award in accordance with FAR 52.217-4: Evaluation of Options Exercised at time of award or anytime during the base period of performance. The option for increased quantity, if exercised, shall be completed with the base period of performance. See Subtask 1.9 below for details on this optional requirement.

Optional Specimen SC-B5 shall have dimensions and reinforcement identical to Specimen SC-A1, except the column longitudinal bars shall be bent into the slab-column joint rather than away from it (Figure 1.7). Simulated gravity loading shall be nominally identical to that for Specimen SC-A1.

Figure 1.7 – Elevation of slab-column connection for Optional Specimen SC-B5.

Subtasks

Subtask 1.1: Define Test Apparatus, Instrumentation, Loading Protocols

The Contractor shall submit drawings that define the test apparatus that will be used to conduct the simulated gravity loading protocol for all slab-column test specimens, including:

the overall geometry of the test specimens and the apparatus that will be used to support and load the test specimens; the planned dimensions including the value of the dimension r that will be used for the various test specimens; the height of the column stubs; shop drawings for each of the test specimens with special attention to reinforcement detailing and concrete placement; the instrumentation plan including types of instruments and their locations; the data acquisition system; and the simulated gravity loading protocol.

The Contractor shall convene a virtual meeting with NIST to describe the aforementioned details. Within five business days, NIST will either approve the proposed details or will provide written comments with recommended modifications to better accomplish the NIST objectives.

The Contractor shall respond to the recommended modifications in writing within ten business days of receiving NIST’s recommended modifications. The Contractor and NIST shall work in good faith to arrive at a mutually agreeable set of testing details.

Subtask 1.2: Fabricate Test Apparatus, Acquire Materials, and Make Test Batch

The apparatus, materials, and test specimen details required by this subtask shall be in accordance with testing details approved by NIST as required by Subtask 1.1.

The Contractor shall acquire materials for the test apparatus, for fabrication of all slab-column test specimens, and instrumentation for all slab-column test specimens. Concrete materials will be provided by NIST. The Contractor shall arrange for transportation of the coarse and fine aggregates and cement from a location in Miami, where the materials are stored by NIST, to the Contractor’s test laboratory (see Appendix B). All other materials are the responsibility of the Contractor.

The Contractor shall make a test batch of the slab concrete following the procedures provided by NIST to gain experience with batching and mixing the specified concrete mixture and to verify that the mixture produces the intended slump and hardened mechanical properties. The Contractor shall make concrete cylinders and shall conduct compressive strength tests at ages 7 days, 14 days, and 28 days and split cylinder tests at 28 days, so that expected strength gain with time can be observed. The cylinders from the test batch shall be sealed at 60 F – 80 F and stripped after 24 hours. The cylinders shall then remain immersed in a 73 F limewater bath until testing at ages 7 days, 14 days, and 28 days.

The Contractor shall prepare the test setup for use in all slab-column test specimens.

Subtask 1.3: Construct Specimens SC-A1, SC-A2, SC-A3, and SC-A4

Casting concrete for this task shall not be done until the test batch tests of Subtask 1.2 are completed.

The Contractor shall install electrical resistance strain gauges on reinforcement, fabricate reinforcement cages, and cast test specimens SC-A1, SC-A2, SC-A3, and SC-A4, along with a sufficient number of concrete cylinders for materials characterization as required elsewhere in this document. Slab-column test specimens shall be cured for 7-14 days, or as required to best achieve the target concrete compressive strength at time of final testing. Concrete cylinders shall be cured with the slab-column test specimens and shall receive a nominally identical curing regime.

Acceptance of the specimens shall be based on inspection of specimens, both prior to and after concrete placement, by the NIST COR at the Contractor’s facility. The Contractor shall also provide the opportunity for NIST to observe placement and consolidation of concrete.

Well into the test specimen curing period, the Contractor shall convene a virtual meeting with NIST to describe progress on acquiring materials, fabricating the test apparatus, construction of the test specimens, and early results of the concrete cylinder tests. The Contractor shall inform NIST of the planned specimen testing schedule and make arrangements for enabling NIST to monitor the tests both in-person and remotely by video and audio broadcast over the Internet.

Subtask 1.4: Conduct Tests on Specimens SC-A1 and SC-A3 and Propose Preloading Protocol for Specimens SC-A2 and SC-A4

The Contractor shall conduct the simulated gravity loading tests on Specimens SC-A1 and SC-A3 in accordance with the testing protocol. The gravity loading tests shall be accompanied by materials tests, including UPV measurements, compression tests, and split cylinder tests, on companion cylinders cast with the test specimen and cores removed from the test specimen, as described elsewhere in this document.

Upon completion of the loading tests, the Contractor shall prepare a brief written letter report summarizing the tests and using those test results to propose a simulated gravity preloading protocol for Specimens SC-A2 and SC-A4. The purpose of the simulated gravity preloading protocol is to cause extensive cracking without significant risk of failure prior to conducting the accelerated corrosion protocols for Specimens SC-A2 and SC-A4. The letter report shall be submitted to NIST and the Contractor shall arrange a video conference with NIST to present the test results and the proposal for the simulated gravity preloading protocol for Specimens SC-A2 and SC-A4. The Contractor and NIST shall agree on the simulated gravity preloading protocol during the video call or shall arrange for a subsequent video call within five business days.

Subtask 1.5: Conduct Tests on Specimens SC-A2 and SC-A4

This Subtask shall not be started until the completion of Subtask 1.4.

The Contractor shall conduct the simulated gravity preloading tests on Specimens SC-A2 and SC-A4, following the simulated gravity load testing protocol, but limiting the loads to values agreed upon in Subtask 1.4.

Following the simulated gravity preloading tests, the Contractor shall work with the NIST Corrosion Contractor, through the NIST COR, to conduct the accelerated corrosion tests on

At the completion of the accelerated corrosion tests on Specimens SC-A2 and SC-A4, the

Contractor shall conduct the simulated gravity loading tests on Specimens SC-A2 and SC-A4 in accordance with the testing protocol.

The tests shall be accompanied by materials tests, including UPV measurements, compression tests, and split cylinder tests, on companion cylinders cast with the test specimen and cores removed from the test specimen, as described elsewhere in this document.

Upon completion of the simulated gravity loading tests to failure, the Contractor shall break the test specimen apart to enable measurement of the degree of corrosion (as measured from gravimetric loss in weight of typical No. 5 and No. 7 bars in the failure zone) and loss of rib profile of typical No. 5 and No. 7 bars in the failure zone.

Upon completion of the tests, the Contractor shall prepare a brief written letter report summarizing and comparing the tests on SC-A1, SC-A2, SC-A3, and SC-A4. The letter report shall be submitted to NIST and the Contractor shall arrange a video conference with NIST to present the test results. The Contractor and NIST shall discuss the merits of targeting various different degrees of corrosion in the later testing of Specimen SC-B1.

Subtask 1.6: Construct Specimens SC-B1, SC-B2, SC-B3, and SC-B4

This Subtask shall not commence until the completion of Subtask 1.4, with the exception that electrical resistance strain gauges may be attached to reinforcement before the completion of Subtask 1.4. This is done to enable minor adjustments to the program considering observations from Subtask 1.4.

The Contractor shall install electrical resistance strain gauges on reinforcement, fabricate reinforcement cages, and cast test specimens SC-B1, SC-B2, SC-B3, and SC-B4, along with a sufficient number of concrete cylinders for materials characterization as required elsewhere in this document. Slab-column test specimens shall be cured for 7-14 days, or as required to best achieve the target concrete compressive strength at time of final testing. Concrete cylinders shall be cured with the slab-column test specimens and shall receive a nominally identical curing regime.

Acceptance of the specimens shall be based on inspection of specimens, both prior to and after concrete placement, by the NIST COR at the Contractor’s facility. The Contractor shall also provide the opportunity for NIST to observe placement and consolidation of concrete.

Well into the test specimen curing period, the Contractor shall convene a virtual meeting with NIST to describe progress on construction of the test specimens and early results of the concrete cylinder tests. The Contractor shall inform NIST of the planned test specimen testing schedule and make arrangements for enabling NIST to monitor the tests remotely by video and audio broadcast over the Internet.

Subtask 1.7: Conduct Tests on Specimens SC-B1 and SC-B4

Following the completion of Subtask 1.5, the Contractor shall convene a virtual meeting with NIST to discuss the merits of different testing protocols for Specimen SC-B1 and SC-B4. At the time of this writing, NIST intends that Specimens SC-B1 and SC-B4 will be subjected to simulated gravity preloading tests intended to damage but not fail the specimen, followed by the accelerated corrosion protocol to an agreed-upon degree of corrosion, followed by simulated gravity loading to failure. Results of tests on other specimens, especially those conducted in Subtask 1.5, may indicate that an alternative testing protocol would be more informative and should be followed for Specimens SC-B1 and SC-B4. The Contractor shall perform a testing protocol mutually agreed upon with NIST.

The tests shall be accompanied by materials tests, including UPV measurements, compression tests, and split cylinder tests, on companion cylinders cast with the test specimen and cores removed from the test specimen, as described elsewhere in this document.

Within five business days of completing the virtual meeting, the Contractor shall submit a letter to NIST…