Structural integrity, seismic support, and system mobility

Edit online

The 3932 is structurally designed to be transported, installed, relocated, and operated in customer environments without loss of functionality and without structural failure or cosmetic damage. Equipped with certain features, the 3932 is capable to withstand high magnitude earthquake events without functional degradation during and after earthquake events.

This section addresses environmental conditions or the level that the 3932 tested and verified.

Note: The vibration and shock levels given here are the levels that 3932 tested and verified and not the upper limit of what the system can withstand. If you have any environmental conditions higher than specified here, please contact your IBM® representatives.

There are three shock and vibration levels:

Ruggedness (Fragility)
Operational shock and vibration
Seismic resistance

Ruggedness (Fragility)

Ruggedness relates to a product's ability to withstand the shipping and relocation environments without structural damage. Product ruggedness is assured through shipping shock, vibration, and horizontal impact testing. Passing the test requirements include no short-term and long-term structural and functional degradation. Ruggedness is a key focus item during the new product design phase. Significant analysis and testing efforts are typically associated with new product and subassembly designs to ensure adequate ruggedness for frames, fragile components, and assemblies. To ensure broad protection against shock and vibration, the subassemblies and minimum and maximum system configurations are subjected to unpackaged and packaged testing to cover possible shipping configurations.

Focus on system level or the frame with its drawers installed include:

Excessive deflection of chassis during drop test
Yielding of drawer chassis, frame rails, cages, and subassemblies
Excessive frame transmissibility

Focus on subassembly level or drawers not installed in a frame include:

Heatsink retention
Chip damage due to heatsink loading
Card interconnect damage
Card retention and latching
Card connector fretting wear
Card and cable connectors
Power supply assembly fragility
Cooling components air moving devices
Hinges and doors

Test levels

There are two vibration test profiles:

Sinusoidal at 0.5 g sweep 2 - 200 Hz for a total of 30 minutes
Random vibration for 15 minutes with power spectral density as shown in Table 1.

For system level testing, the system is subjected to vertical direction vibration.

For subassembly testing, the test is conducted on all three perpendicular axes.

Table 1. Truck, air, rail, and ocean vibration spectrum *
Frequency (Hz)	G²/Hz (PSD level)	graph representation
2	0.0010
4	0.0220
8	0.0220
40	0.0022
55	0.0070
70	0.0070
75	0.0220
200	0.0007
Note: * A rms = 0.8044 G, V rms = 4.508 in/s, D rms = 0.1578 in zero to peak

There are two shock test levels:

System level or the frame with its drawers installed – vertical direction
10 times free fall drops at 39.3 in/s velocity change
2 times free fall drops at 55.6 in/s velocity change
Subassembly or drawers level – in all 6 faces
100 g, 3 ms half sine pulse 2x per face
50 g, 11 ms half sine pulse 2x per face

Since 1980, the shock test levels that are previously specified and vibration test levels specified in Table 1 have been utilized. No documented cases of field problems associated with normal shipping shock and vibration exist.

Operational shock and vibration

Operational shock and vibration relates to a product's ability to withstand normal shock and vibration from its installation environments without functional degradation. Although the shock and vibration sources are typically from the surrounding environment (nearby cooling operating equipment, people walking by or dropping materials, etc.), they also can be self-induced (vibration from fans, blowers, compressors, etc.).

Test levels

All the 3932 systems while running are verified to meet the vertical vibration level given in Table 2 and Figure 1 without any functional degradation. The 3932 is verified to be able to withstand five vertical shock inputs 3.5 g with 3 ms half sine pulse width.

Table 2. Random vibration PSD profile breakpoint ¹
Class	5 Hz	17 Hz	45 Hz	48 Hz	62 Hz	65 Hz	150 Hz	200 Hz	500 Hz
V1L/V2	2.0x10^-7	2.2x10^-5	2.2x10^-5	2.2x10^-5	2.2x10^-5	2.2x10^-5	2.2x10^-5	2.2x10^-5	2.2x10^-5
Notes: All values in this table are in g²/Hz. For reference only. No test required.

continuous operational vibration — Figure 1. Continuous operational vibration

Documented cases of field problems associated with externally imposed shock and vibration during normal equipment operation are essentially nonexistent.

Seismic (Earthquake) resistance

In earthquake areas, the 3932 equipped with the appropriate earthquake kits are certified to meet requirements ICC IES AC156.

To achieve the most generally applicable results, the required 5% damped response spectrum (RRS) was based on the worst-case scenario parameters for ground level, as defined by IBC and summarized in Table 3. Using these parameters, the maximum spectral acceleration values, A_FLX-H and A_RIG-H as defined in AC156, were calculated as shown in the following table.

Parameters used for Required Response Spectrum (RRS) math equation

Table 3. Parameters used for Required Response Spectrum (RRS)
Test criteria	S_DS (g)	z/h	Horizontal		Vertical
			A_FLX-H	A_RIG-H	A_FLX-V	A_RIG-V
ICC-ES AC156	2.5	1.0	3.20	3.00	1.68	0.68
Notes: S_DS = Design spectral response acceleration at short period A_FLX-H = Horizontal spectral acceleration calculated for flexible components A_RIG-H = Horizontal spectral acceleration calculated for rigid components A_FLX-V = Vertical spectral acceleration calculated for flexible components A_RIG-V = Vertical spectral acceleration calculated for rigid components

For vertical response, z is assumed to be 0.00 for all attachment heights, which results in the follow:

A set of three, phase incoherent simulated ground motions were derived using a specialty software and based on the RRS parameters previously defined. The duration of the records were set to 30 seconds. In order to achieve the minimum acceleration required specified by ASCE 7, it was ensured that the nominal peak shake-table (ground) accelerations were equal to, or exceeding 0.90 A_RIG-H by introducing a spike in the input acceleration.

The above S_DS parameters 2.5 g represents the high magnitude covering most of densely populated area in California. As an example S_DS values for Los Angeles (1.29 g), San Francisco (2.00 g), Santa Barbara (2.00 g), and San Diego (1.60 g).

In addition, the 3932 was tested to Telcordia NEBS (National Equipment Building Specifications) zone 4 seismic test profile. During and after the test, no system functional interruption was observed with only the front and rear covers opening during testing.

A mainframe computer’s structure consists of a frame or rack, drawers with central processor units, I/O equipment, memory, and other electronic equipment. The focus of this structural mechanical analysis and design is on the frame, earthquake stiffening brackets, and frame tie-down methods. The primary function of the frame is to protect critical electronic equipment in two modes. The first mode is during shipping shock and vibration, which provides excitation primarily in the vertical direction. The second mode of protection is protecting the equipment during seismic events where horizontal vibration can be significant. Frame stiffening brackets and tie-downs are features added to mainframe systems that must meet earthquake resistance requirements. Designing to withstand seismic events requires significant analysis and test efforts because the functional performance of the system must be maintained during and after seismic events. The frame stiffening brackets and anchorage system must have adequate strength and stiffness to counteract earthquake-induced forces, thereby preventing human injury and potential system damage. The frame’s stiffening bracket and tie-down combination must ensure continued system operation by limiting overall displacement of the structure to acceptable levels, while not inducing undue stress to the critical electronic components.

Quality screen (Manufacturing stress screening)

One application of shock and vibration technology that falls outside the design function is manufacturing stress screening and field failure analysis of intermittent subassemblies, such as the 3932 power supplies. By subjecting samples of production subassemblies to screening tests, it is possible to detect certain manufacturing, component, and design problems in these subassemblies. Typical tests include thermal cycling and random vibration, followed by burn-in and functional test at a vendor or subassembly manufacturer.

System mobility

As previously mentioned, all systems are shipped within a fully enclosed wooden and palatalized crate. In addition, the bottom of the system contains two pairs of casters; one pair of fixed casters and one pair of swivel casters. Due to the caster functionality, care must be taken when transporting the system within the wooden crate or when directly rolling the system on its casters.

To ensure safe transportation, a, minimum of 3 people should be available to transport the system. Prior to system relocation, the levers securing the casters must be rotated upward and a maximum of 10^o incline is recommended for all ramped surfaces.