AASHTO Specification for Shock Transmission Units

SECTION 32 SHOCK TRANSMISSION UNITS

Table of Contents SPECIFICATIONS AND COMMENTARY 32.1 GENERAL .....................................................................................................................................32-1 32.2 WORKING DRAWINGS .............................................................................................................32-1 32.3 MATERIALS.................................................................................................................................32-2 32.3.1 Steel ..................................................................................................................................32-2 32.3.2 Internal Fluid...................................................................................................................32-3 32.3.3 Packaging, Handling, and Storage.................................................................................32-3 32.3.4 Manufacture/Fabrication ...............................................................................................32-3 32.3.4.1 GENERAL............................................................................................................32-3 32.3.4.2 CONNECTING HARDWARE ............................................................................32-4 32.3.4.3 CONNECTION TOLERANCES..........................................................................32-4 32.4 TESTING AND ACCEPTANCE .................................................................................................32-4 32.4.1 Prequaliflcations Tests ....................................................................................................32-4 32.4.2 Prototype Tests ................................................................................................................32-4 32.4.2.1 GENERAL............................................................................................................32-4 32.4.2.2 HYDROSTATIC PRESSURE TEST ...................................................................32-5 32.4.2.3 SLOW MOVEMENT TEST (THERMAL)..........................................................32-5 32.4.2.4 FAST MOVEMENT TEST ..................................................................................32-5 32.4.2.5 SIMULATED DYNAMIC TEST.........................................................................32-5 32.4.2.6 OVERLOAD TEST..............................................................................................32-6 32.4.2.7 FATIGUE LOAD TEST.......................................................................................32-6 32.4.3 Proof Testing (Quality Control) .....................................................................................32-6 32.4.3.1 GENERAL............................................................................................................32-6 32.4.3.2 HYDROSTATIC PRESSURE TEST ...................................................................32-7 32.4.3.3 SLOW MOVEMENT TEST (THERMAL)..........................................................32-7 32.4.3.4 FAST MOVEMENT TEST ..................................................................................32-7 32.5 MANUALS.....................................................................................................................................32-7 32.5.1 Installation Manuals .......................................................................................................32-7 32.5.2 Maintenance and Inspection Manual ............................................................................32-8 32.6 MEASUREMENT AND PAYMENT...........................................................................................32-9

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SPECIFICATIONS

COMMENTARY

SECTION 32—SHOCK TRANSMISSION UNITS 32.1 GENERAL

C32.1

This work shall consist of furnishing and installing shock transmission units (STUs) and hardware for attaching to bridge structures. STUs and hardware shall be constructed in accordance with the details shown in the contract documents and these specifications. When complete details are not provided, STUs and hardware shall be furnished that conform to the limited details shown in the contract documents and shall provide the design capacities for minimum and maximum loads and movements, and the performance characteristics specified.

A Shock Transmission Unit (STU) is a fabricated component that is designed to be connected between bridge members which moves freely when loads are slowly applied such as would be caused by temperature changes, but acts as a rigid link capable of transmitting a force under rapidly applied loads caused by vehicle braking or impact and earthquakes.

32.2 WORKING DRAWINGS Whenever complete details for STUs and hardware are not shown in the contract documents, the Contractor shall prepare and submit working drawings for the STUs and hardware. Such drawings shall show the external details and dimensions of the STUs and hardware proposed for use and shall be approved by the Engineer prior to fabrication. Such approval shall not relieve the Contractor of any responsibility under the contract documents for successful completion of the work. The following shall be specified on the working drawings: •

The total number of ST(Js required, grouped according to rated capacity and rated travel limits.

•

The mass of each STU.

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The plan view and section elevation view showing all relative dimensions, including dimensions for the assumed installation temperature, of each STU and attachment hardware.

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The minimum and maximum design temperatures of the STUs.

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The maximum drag force at the specified rate of movement caused by the specified temperature changes for each STU.

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The total movement capacity of each STU.

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32.3

SPECIFICATIONS •

The maximum rated load capacity for each STU.

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The maximum movement anticipated for each cycle during dynamic loadings.

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The type of materials to be used for all STUs and attachment hardware.

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Painting or coating materials to be applied.

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Alignment plans for the STUs showing tolerances for alignment in which the STUs must be installed.

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Installation schemes.

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Design calculations for the attachment hardware verifying conformance with the loading requirements, if required by the contract documents.

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Anchorage details of the attachment hardware.

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The place of manufacture of the STUs and the fabricator of the hardware.

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The Manufacturer’s name and the name of the representative who will be responsible for coordinating production, inspection, sampling, and testing.

COMMENTARY

32.3 MATERIALS 32.3.1 Steel

C32.3.1

Unless noted otherwise in the contract documents, attachment hardware shall meet the requirements of AASHTO M 270M (ASTM A 709M), Grade 345 steel. All other metal components of the STU, except for the piston rod, shall meet the requirements of AISI 1026, or equivalent. The piston rod shall meet the requirements of ASTM A 240M, Type 304L, stainless steel, or equivalent. Bolts shall meet the requirements of AASHTO M 164M (ASTM A 325M), Type 1, unless noted otherwise in the contract documents.

The corrosion protection system used on STUs should be the same as used on the bridge. Uncoated weathering steel is preferred to reduce maintenance requirements. However, STUs can be furnished with a standard galvanized finish on all exposed parts. The boot protecting the piston rod is made of a durable reinforced neoprene material. The stainless steel piston rod is protected by grease packed into the neoprene boot. It is the responsibility of the designer to determine if this protection “package” is satisfactory for the exposure conditions expected over the service life of the STU. If additional protection is required, it shall be so noted in the project special provisions. If specific durability testing is required as a condition of acceptance, the requirements shall be so specified by the designer as a part of the order. Particular attention must be directed to whether corrosion protection beyond that provided for other bridge components is necessary for the anchorage system(s). Environmental conditions to be considered are: •

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Coastal (marine salts)

Materials

Section 32—Shock Transmission Units

SPECIFICATIONS

COMMENTARY

32.3.2 Internal Fluid

•

Industrial

•

Potential for periodic immersion due to flooding

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Deicing salts and mud (under bridge joints)

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Inadvertent sandblasting during repainting

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Pigeon nests

•

Ultraviolet light and ozone exposure of neoprene

The Manufacturer shall determine the fluid used inside the STU to provide the shock resistance capacity of the STU. Where this material is proprietary in nature, the contract documents shall specify that the Manufacturer demonstrate through the testing program that the design requirements of the STU can be met. The operating fluid used in the STU shall be OSHA approved non-toxic nonflammable silicone-based fluid or putty. The Manufacturer shall provide a certification that the material in each STU is the same material as was used in the testing program. 32.3.3 Packaging, Handling, and Storage Prior to shipment from the point of manufacture, STUs shall be packaged in such a manner to ensure that during shipment and storage, the STUs will be protected against damage from handling, weather, or any normal hazard. Each package shall be marked to clearly note the STU identification number, the rated capacity, the Manufacturer’s name, and the project identification. All STUs shall be stored at the work site in an area that provides protection from environmental and physical damage. When installed, STUs and hardware shall be clean and free of all foreign substances. Dismantling of STUs at the site shall not be done unless absolutely necessary for inspection or installation. STUs shall not be opened or dismantled at the site, except under the direct supervision of, or with the approval of, the Manufacturer. 32.3.4 Manufacture/Fabrication 32.3.4.1 GENERAL The Manufacturer shall certify that each STU satisfies the requirements of the contract documents and these specifications. Each STU shall have stamped on the body the STU identification number, the rated capacity, the

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SPECIFICATIONS

COMMENTARY

Manufacturer’s name, and the project identification. STUs. including the attachment hardware, shall be preassembled in the shop by the Manufacturer and checked for proper completeness, tolerances, and geometry before shipping to the site. 32.3.4.2 CONNECTING HARDWARE Hardware used to connect the STU to the substructure and/or superstructure shall be fabricated in accordance with Section 11, Steel Structures. 2.3.4.3 CONNECTING TOLERANCES Differences between pin and hole diameters shall be 250 µm maximum.

C32.4

32.4 TESTING AND ACCEPTANCE

The testing requirements and service life of the device are to be chosen by the designer, and can be 25 to 75 years, subject to the appropriate maintenance being performed by the owner. If a particular application requires a significantly longer or shorter service life, appropriate modifications to the test requirements for a fatigue life should be considered.

All shock transmission units shall be tested to verify their performance and design properties under slow movement, fast movement and cyclic loading. In general, there are three types of tests to be performed on an STU: •

Prequalification test (system characterization tests) described in Article 32.4.1;

•

Prototype tests, described in Article 32.4.2;

•

Proof tests (quality control tests) described in Article 32.4.3

32.4.1 Prequalification Tests

C32.4.1

The performance and fundamental properties of the STU shall be verified by testing before it can be adapted for use. These tests include component tests of individual units, assembled units, and scaled structure complete with STUs. At a minimum, these tests shall be conducted according to the testing guidelines developed by the Highway Innovative Technology Center (HITEC) evaluation panel.

These prequalification tests usually are not project specific. They are conducted to establish the properties of the unit when a new STU is being developed or a substantially different version of an existing unit is being evaluated.

32.4.2 Prototype Tests C32.4.2.1

32.4.2.1 GENERAL

The objectives of these tests are to evaluate the performance of STUs for two design conditions consisting of slow movements that will not lock-up the device, and fast movements that will lock-up the device within temperature and loading conditions at least equal to those at the project site.

The resistance and the stroke under slow movement and the lock-up force under fast movement of the STU used in the design and in the analysis shall be verified by prototype tests. All testing shall be performed at an independent testing laboratory approved by the Engineer. All testing shall be performed in the presence of the Engineer unless otherwise

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32.4

Section 32—Shock Transmission Units

SPECIFICATIONS

COMMENTARY

approved in writing by the Engineer. These tests can be conducted at ambient temperature. The prototype tests identified herein shall be performed on at least one STU of each type. 32.4.2.2 HYDROSTATIC PRESSURE TEST The STU shall be tested for at least 3 minutes at 150 percent of the maximum computed internal pressure to verify the structural integrity of the high pressure boundary. The STU shall be pressurized and sealed for the duration of the test. Initial and final pressure readings shall be recorded. ACCEPTANCE: No signs of leakage under pressure. Hydrostatic pressure shall not drop more than 5 percent during the test. C32.4.2.3

32.4.2.3 SLOW MOVEMENT TEST (THERMAL)

Nominal rated force of the STU is defined as PR.

The STU shall be cycled for three complete and continuous cycles at a low velocity and a maximum stroke specified by the Engineer to verify the operation and travel of the unit. A continuous plot of the load and deflection shall be recorded. ACCEPTANCE: No sign of leakage under operation. No sign of structural binding under operation. The force required to cycle the unit shall not exceed 10 percent of the nominal rated force or as specified by the Engineer. The STU shall not lock-up during this test. 32.4.2.4 FAST MOVEMENT TEST The STU shall have the full nominal rated force applied to it at a fast travel rate specified by the Engineer. The STU shall be tested in both compression and tension, but testing need not be cyclic. A continuous plot of load versus deflection shall be recorded. ACCEPTANCE: The STU shall lock-up within 12 mm or as specified by the Engineer of the point of zero movement. The lock-up deflection shall be taken as the deflection at which a constant stiffness is achieved. The deflection from the point of lock-up to the maximum test load shall not exceed 12 mm or as specified by the Engineer. The stiffness of each STU throughout the force range from lock-up to maximum test load shall not vary by more than 10 percent. Unit shall show no sign of leakage or binding. 32.4.2.5 SIMULATED DYNAMIC TEST The STU shall be tested to determine the ability of the unit to lock-up during dynamic loads. Each unit will have tension force applied in less than 0.5 seconds or as specified by the Engineer; this force will be sustained for the

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SPECIFICATIONS

COMMENTARY

period of five seconds. At the end of the five seconds of tension load, the unit shall be put into compression within one second or as specified by the Engineer. The compression force will be held for five seconds. The tension and compression force shall be equal and will be at least three times the lock-up force determined in Article 32.4.3.4, Fast Movement Test, but no more than the nominal rated force. A continuous plot of force versus deflection shall be recorded. ACCEPTANCE: Deflection between the point of zero load and the point of maximum load shall not exceed 12 mm or as specified by the Engineer, in either the initial loading stage or in the force reversal stage. Deflection during the sustained load portion of the test shall not exceed 12 mm or as specified by the Engineer. C32.4.2.6

32.4.2.6 OVERLOAD TEST

The purpose of this test is to ensure the STU will perform properly should the nominal rated force be exceeded while in service.

The STU shall be loaded by 1.5 times the nominal rated force at a rate fast enough to make the unit lock-up, then hold the load for 30 seconds or as specified by the Engineer. ACCEPTANCE: Unit shall show no sign of leakage or binding.

C32.4.2.7

32.4.2.7 FATIGUE LOAD TEST

The purpose of this test is to determine if the STU can withstand as many cycles of load as could occur from braking on a highway bridge with high vehicle braking actions. The “worst case” scenario for service loading of STUs is an application of braking loads equal to the “lock-up load” four times a day, for the AASHTO LRFD specified design life of 75 years. This is roughly equivalent to 100,000 load cycles. (4 cycles/day * 365 days/year * 75-year service life = 109,500; use 100,000). See AASHTO LRFD Bridge Design Specifications. Article 3.6.4, for “BR” force and application.

The STU shall be cycled for 100,000 complete and continuous cycles at a velocity (frequency) specified by the Engineer and a load equal to the nominal rated force (PR) of the STU. ACCEPTANCE: Unit shall show no sign of leakage or binding.

32.43 Proof Testing (Quality Control) 32.4.3.1 GENERAL These tests shall be conducted on every STU that is going to be incorporated into the structure. All testing shall be performed at an independent testing laboratory approved by the Engineer. All testing shall be performed in the presence of the Engineer unless otherwise approved in writing by the Engineer. These tests can be conducted at ambient temperature. The proof tests shall consist of the following.

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32.4

Section 32—Shock Transmission Units

SPECIFICATIONS

COMMENTARY

32.4.3.2 HYDROSTATIC PRESSURE TEST The STU shall be tested for at least three minutes at 150 percent of the maximum computed internal pressure to verify the structural integrity of the high pressure boundary. The STU shall be pressurized and sealed for the duration of the test. Initial and final pressure readings shall be recorded. ACCEPTANCE: No signs of leakage under pressure. Hydrostatic pressure shall not drop more than 5 percent during the test. 32.4.3.3 SLOW MOVEMENT TEST (THERMAL) The STU shall be cycled for three complete and continuous cycles at a low velocity and a maximum stroke specified by the Engineer to verify the operation and travel of the unit. A continuous plot of the force verses deflection and force verses time shall be recorded. ACCEPTANCE: No sign of leakage under operation. No sign of structural binding under operation. The force required to cycle the unit shall not exceed 10 percent of the nominal rated force or as specified by the Engineer. The STU shall not lock-up during this test. 32.4.3.4 FAST MOVEMENT TEST The STU shall have the full nominal rated force applied to it at a fast travel rate specified by the Engineer. The STU shall be tested in both compression and tension, but testing need not be cyclic. A continuous plot of load versus deflection shall be recorded. ACCEPTANCE: The STU shall lock-up within 12 mm or as specified by the Engineer of the point of zero movement. The lock-up deflection shall be taken as the deflection at which a constant stiffness is achieved. The deflection from the point of lock-up to the maximum test load shall not exceed 12 mm or as specified by the Engineer. The stiffness of each STU throughout the force range from lock-up to maximum test load shall not vary by more than 10 percent. Unit shall show no sign of leakage or binding.

32.5 MANUALS 32.5.1 Installation Manuals The Manufacturer shall provide an installation manual which includes specific instructions to ensure proper installation procedures for the STU. The following items shall be included: •

Name of the Manufacturer’s representative who will provide assistance and advice during installation of the STUs.

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32.4

SPECIFICATIONS •

Alignment dimensions, installation temperature, and the “ideal” installation length of the device.

•

Details of any required installation equipment and complete procedures, including installation tolerances, as well as instructions on its use.

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Shop drawings of the STUs and the connections to the bridge components, including tolerances for critical components and connection details.

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STU job site storage requirements while awaiting installation.

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STU electrical isolation procedures where there is a possibility of galvanic or electrolytic corrosion occurring.

COMMENTARY

32.5.2 Maintenance and Inspection Manuals The Manufacturer shall provide a manual that will include specific instructions to ensure proper maintenance and inspection procedures for the STUs while in service. The following items should be included: •

Information as to what to inspect, and what to look for (i.e. pull back piston rod covering, if used, and look for evidence of leakage). Include any precautions necessary to avoid damage to the boot and device.

•

Information on type of grease to apply to the exposed piston rod and frequency of application.

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Instructions on how to check the inspection holes, greasing points, etc.

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Instructions for “removal and replacement” of the STU, including schematics of any special equipment needed.

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When required by the contract documents, details of any necessary tools and equipment shall be provided to allow the STU to be proof tested to verify movement capability while on the structure.

•

Instructions for each inspection (generally assumed to be at a frequency of two years) and after each significant seismic event shall include at least the following: •

Perform a visual inspection of the anchorage system to ensure it is not damaged.

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32.6

Section 32—Shock Transmission Units

SPECIFICATIONS •

Determine need for maintenance forces to clean the STIJ and its anchorages to prevent accelerated corrosion.

•

Determine need for repainting/recoating of the device.

•

All STUs on the bridge shall be closely inspected for signs of leakage. If leakage is noted when inspecting the boot, notify maintenance forces to remove boot and inspect piston rod for damage.

•

Inspect for unexpected changes in alignment or condition that would indicate the STU experienced unexpected force application; etc.

•

Every six years, or as determined by the owner, notify maintenance forces to unclasp the protective boot and examine the condition of the piston rod, as well as determine if there is evidence of leakage of the internal fluid.

•

Every ten years notify maintenance forces to load STU(s) as selected by the owner, and in a manner to ensure the STU can develop the rated load.

COMMENTARY

32.6 MEASUREMENT AND PAYMENT

C32.6

STUs shall be measured and paid for by the number of units installed and accepted as shown in the contract documents or ordered by the Engineer. The contract unit price paid for “Shock Transmission Units” shall include full compensation for furnishing all labor, materials, tools, equipment and incidentals, and for doing all the work involved in installing STUs (including testing), complete in place, as specified in these specifications, the contract documents, and as directed by the Engineer.

Some agencies prefer to pay for testing separately, especially if waiver of testing is a consideration.

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