工程合約BIM要求 - 高手只關心BIM USES

同工程界嘅朋友傾起BIM，好多時都會出現以下嘅對話﹕ "單嘢LOD畫幾多？" "有幾多個clashes? Solve晒未？要零clashes喎。" "係唔係要做埋5D, 6D, 7D, 8D…？" 如果對BIM嘅認識仲停留响上述講法，就係時候要更新一下。 先講LOD。筆者於前文<Conceal Conduit需唔需要BIM>已提及過，早於CIC MEP BIM Standards (2019 version)，已經將LOD分拆成 LOD-Graphic (LOD-G) , LOD-Information (LOD-I) 及 DOC。LOD-G係先係描述緊個elements要model到有幾細緻，如圖﹕ 而LOD-I，係描述緊個element嘅資料有幾詳盡，如圖﹕ DOC 係 Level of Documentation，即係個 BIM 嘅 DOC 應該包括埋 Catalogue, O&M Manual, Test Report, Warranties, Statutory…etc., 如圖﹕ 即使係去到As-Built Stage，CIC MEP BIM Standards (2019 version) 只建議 LOD-G 去到300。最主要係考慮到modelling太多細節位的話，個BIM file size會好大，好多電腦硬件行唔到；當然，LOD-I 就建議去到500。所以，以後大家講LOD嘅時候，最好講清楚係LOD-G or LOD-I。

站於Client PM嘅角度，佢地好多時對LOD-G畫到有幾精細係唔會太關心，只要件嘢畫出嚟大概分辨到係啲乜就得；佢地真正關心嘅係件嘢係唔係跟足approved嘅物料嚟畫、畫得齊唔齊(如congested area嘅hangers)、夠唔夠空間運送、安裝及維修等等；至於LOD-I，就真係要入資料入得足，因為日後FM嘅同事真係要用到。

至於clashes方面，一般 Consultancy Agreement 或 Main Works Contract 的確係會寫死”Clashes Free” or “Zero Clashes”。至於撞5mm算係一個clashes，定係50mm先算係？暫時香港或國際用開嘅Standards or Guidelines都冇定義過，普遍做法會set 25mm ~ 50mm 之間。但站於工程項目PM嘅角度，佢地關心嘅唔係clashes個數字，而係落到場啲嘢係唔係真係夠位裝、夠位日後maintenance。筆者認為比較好嘅做法係，為呢堆clashes嘅重要程度分類，如下表﹕

Clashes Category		Description
1	Design Issues	需要顧問改設計先解決到嘅問題
2	Coordination Issues	判頭自己夾圖後可解決嘅問題，不涉及設計改動
3	Modelling Issues	BIM modeller 手文之誤、或BIM軟件之問題，可簡單解決

最優先解決係1.，即係牽一髮會動全身嘅問題。有時為咗解決個clashes，係要改原有設計，可能又因為改完呢個設計，會有新clashes嘅出現，所以務必提前解決；至於歸類為2.及3.嘅clashes，一般留返比判頭自己解決就得。 至於5D, 6D, 7D, 8D…發展局好多年前已經決定棄用上述講法。原因係，5D以前(如 4D = Time，5D = Cost)有較好嘅共識，但5D以後係啲乜，幾乎無共識。所以發展局2017年第一封關於BIM嘅Technical Circular開始，甚至到最新嘅2023年Technical Circular，都係用20項BIM Uses嚟劃分個BIM究竟應該要點用﹕

	BIM Uses	DevB TC 2023 Design Stage	DevB TC 2023 Construction Stage
1	Design Authoring	Mandatory	Mandatory
2	Design Reviews	Mandatory	Mandatory
3	Existing Conditions Modelling	Mandatory	Mandatory
4	Site Analysis	Mandatory	N/A
5	3D Coordination	Mandatory	Mandatory
6	Cost Estimation	Mandatory	Mandatory
7	Engineering Analysis	Mandatory	Mandatory
8	Facility Energy Analysis	Optional	Optional
9	Sustainability Evaluation	Mandatory	Mandatory
10	Space Programming	Mandatory	N/A
11	Phase Planning (4D Modelling)	Mandatory	Mandatory
12	Digital Fabrication	Mandatory	Mandatory
13	Site Utilization Planning	N/A	Mandatory
14	3D Control and Planning	N/A	Mandatory
15	As-Built Modelling	N/A	Mandatory
16	Project System Analysis	N/A	Optional
17	Maintenance Scheduling	N/A	Mandatory
18	Space Management and Tracking	N/A	Optional
19	Asset Management	N/A	Mandatory
20	Drawing Generation	Mandatory	Mandatory

上述三個講法其實都已經包含咗响呢廿個BIM Uses入面。如LOD與3., 5., 15.~19.等有關；Clashes與5.有關；5D同6.有關；其餘6D, 7D, 8D…即係一系列未有共識嘅BIM Uses。

DevB TC 2020年開始嘅BIM KPI，都只係以BIM Uses嚟劃分﹕ 一般嚟講，合約BIM Specification嘅BIM Uses會寫到好虛，舉一例，第14項 BIM Uses 嘅 3D Control and Planning，一般會咁寫﹕
"For a large-scale project requiring Digital Works Supervision System, the Contractor shall utilize the BIM model for digital setting-out, construction checking, etc. as appropriate by means of 3D laser scanners, robotic total stations, etc. as far as practicable."

究竟個3D laser scanners要點用法？全個地盤任何setting out，包括開大墨、裝地渠、釘板留窿、砌牆...等等都要用？As far as practicable應該點理解？一個地盤咁多個位同時做緊嘢，而一台機幾十萬又要有受過專業訓練嘅人先識用，要求判頭成個地盤都用3D laser scanners又合唔合理? 抑或用嚟覆核一次墨斗哥哥條數已經算係做到呢個BIM Uses?

呢個時候，就係BIM Execution Plan BEP出場嘅時間。業主、顧問、判頭，可以基於地盤實際嘅需要，由判頭於BEP提出實現呢項BIM Uses嘅詳盡方法及應用範圍，然後上比顧問做approval，而呢份BEP就會以新嘅合約形式出現 (舊嘅合約係BIM Specification，新嘅合約係BEP；BEP係基於BIM Specification嘅原則而制定)。當然，BEP係一份 living document [1] 嚟，業主或顧問可以跟據實際情況要求判頭更新該文件並再次提交審批。

[1]: Living document is a document that is continually edited and updated.