Case Study: L3 Screening Machine Replacement – Riyadh Airport
Preliminary design assessment of the existing steel frames to check the current design conditions. Structural analysis and design calculations for all steels and reinforcements where required. Steel connection designs and verifications. Quantity, weight of each part of additional steel and modeling by design program.
In December 2019, CAS Structure did a project with Riyadh Airport in coordination with Arafat Construction & Metal Ind., where the client’s main concern was the vibration effects and deflections of the existing floor system due to replacement of the existing machine to a heavier equipment. CAS Structure had the privilege to follow on the task of engineering calculations and provide solutions to address the concerns.
In site visits for the structural analysis, CAS Structure teams observed:
- The structural elements for the slab carrying the machines consists of steel platform structure (I-Beams sections) and grating fixed on existing concrete structure and the top slab consists of TT pre-cast slab.
- According to the observations, the (TT-slab) which is the roof of the screening machine cannot carry fixed hanging permanent crane additional point load of approximately 8 tons. This is based on preliminary assessment of the TT-slab which is already verified in details.
The HI-SCAN 10080 XCT machine is seated on 30 stands, weight of which ranges from 140
kg to 483 kg. Vibration is transmitted through 6 stands only. The four parts of the machine are also reflected. The figures show point load per stand as well as load per 75 cm square.
Structural Design Criteria
Structural design criteria that will be considered in the design verification of the steel platform
pertaining to the new SD screening machine are:
- Maximum static deflection of the floor girders 1.0 mm/m (L/1000)
- Permissible ground vibration 0.3 mm/s (1Hz to 80Hz)
Structural Details of the Project
- Structural details of existing slabs including grating details, structural steel beams and details, reinforced concrete beams and details, columns and foundation details and related calculation are already verified as well as structural information, including framing plans, reinforcement plans and R.C. details, pertaining to adjacent slabs as well where the screening machine will have eventually to be dismantled and replaced. This includes structural details of the TT precast slab and adjacent slab system including supporting cast-in-situ main framing beams.
- Support conditions of the new screening machines; i.e. will it be directly seated on the slab, I-beams, grating, etc. Smith Detection has provided technical specifications regarding the working conditions of the equipment, especially XCT emits the Vibrations and this must be taken into consideration with the vibrations emitted by the BHS equipment (conveyors and motors) and 2nd XCT on the same platform to not exceed Permissible vibrations and maximum Static Deflection, applicable for all directions.
CAS Structure scope consisted of structural verification of the existing steel platform at KKIA Terminal T5 supporting the X-Ray screening machines since it is required to replace the Examiner XLB L3 machines with Smiths Heiman HI-SCAN 10080 XCT which are heavier and have different structural requirement for proper and accurate performance.
Finite element Model has been created to simulate the structural properties of the steel platform supporting the screening machines including geometry, member properties and sections, loading applied to the structure including super imposed dead load, live load and screening machine loads static and dynamic loads.
Members sections adopted in the analysis were collected from the as-built structural drawings provided by Riyadh Airport Company (RAC) for the X-Ray steel platform.
Steel grating and checker plates are used to cover the members and bridge the span between beams and to ensure proper ventilation of the volume as deemed necessary for the operation of the X-Ray machines.
The finite elements simulation model has been executed to verify the structural adequacy of the steel platform based on occupancy and machine loads as for strength and serviceability requirements. Members’ strength is verified based on the stress check ratio of the applied straining actions to member capacity which shall be less than 1. Otherwise, strengthening would be necessary. Also, deformation of the platform shall satisfy stringent requirements of the SD machine of L/1000 allowable deflection; that is 1mm for every 1m span; which is a stricter requirement than international building code requirements where L/480 allowable deflection values are adopted.
CAS Structure came up with the solution to introduce additional steel beam support in between existing steel beams and increasing the existing steel plate platform thickness such that the point loads are distributed evenly across the steel plate platform and transferred on to each of the supporting steel beam.