第三十九期《BIM 手册》第二章_2.3.5节——构件管理和链接

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构件管理

BIM模型变得相当大且复杂。几个GB大小的模型越来越常见。这种情况下，数据协调和管理（这在第三章中被称为“同步”）成为了一种大量数据管理任务和难题。传统方法使用文件更新项目版本会导致两类问题：

1.    文件量变得巨大，必须把项目以某种方式分块以继续完成设计；文件很大、运行缓慢且笨重。

2.    确定文件中的变更依然是手动管理工作，把在图纸上用红色马克笔写注释变成在3D PDF或相似文件上写注释。传统上，不能在准备施工文件阶段做出大的变更，因为那样成本过高。BIM和模型管理可以剔除或大大降低这方面的问题。尽管参数化更新解决了局部变更的问题，但是不同模型之间的协调和模型中用于规划、分析和报告的数据依然是一个重要且日益突出的问题。

长期以来一直强调但直到最近才在使用环境特别是ArchiCAD’s Delta BIM server（详见第三章，3.5.3节）实现的功能是，仅在文件中交换新的、修改过的或者删除的构件实例，就会剔除未修改构件中的问题。只传递变更的构件并将其载入（即增量更新），这会大大地降低交换文件的大小，且能立刻识别并找出变更问题。此功能需要构件级别的构件识别和版本控制，这通常由时间戳提供。随着BIM模型文件变大，这一功能将会变得越来越重要。这一特性将在未来发布的所有系统中成为必备，用以在多个BIM应用程序之间协调。

外部参数管理

在大量创造性项目中所探讨的一项功能是，基于电子表格中生成并定义的控制参数（通常是3D网格）来控制设计的参数化布局。在第五章中的建筑核心模型和第九章中的Aviva Stadium案例研究中同时列举了使用电子表格来控制并协调几何图形的应用程序案例。

对某些类型的项目，从电子表格中读写的能力在一定层面上为不同设计工具之间提供了互操作性。假设可以用同样的参数控制几何图形，在两种不同建模环境（例如Rhino 和 Bentley）中创建等体量的参数化模型。可以在Rhino（一款对用户友好但信息有限的设计工具）中做设计方案推敲，然后把参数更新到Bentley中，以便将变更整合到可能包含成本和能量分析功能的BIM工具中。电子表格提供了一种重量级的几何图形互操作性。

参数列表的外部参数电子表格的另一个用途是通过参照而不是明确地交换参数化构件。最广为人知的例子是钢结构。电子版的钢材手册带有结构钢的不同标准的截面轮廓，例如W18×35或L4×4。这些轮库名称可用于检索钢材手册中的轮廓、重量以及体量属性。类似的轮廓也可用于预制混凝土产品、配筋以及窗户制造商的目录。

如果发送者跟接受者都能访问同一个目录，然后他们可通过参照（名称）发送并检索相关信息，并且这种交换是通过检索适当目录信息并将之载入到适当的参数化模型中来实现的。这在许多生成领域中是一个很重要的功能。

链接到外部目录文件

另一个重要功能是为外部文件提供链接。目前这种功能的主要应用于将产品链接到与之相关的手册进行维护和运行，以便于后期与设施运行&维护(O&M)相关联。有些BIM工具能实现这项功能并作为能为运维阶段提供支持的工具加强其价值。

本节列举的这些功能对于评估、选择BIM平台来说都很重要。稍后我们将在本章用这些功能来评估主要的BIM设计工具。

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Object Management

BIM models become quite large and complex. Multigigabyte models are becoming common. In such cases data coordination and management (what is called “synchronization” in Chapter 3) becomes a large data management task and concern. The traditional approaches to updating versions of  a  project  using files leads to two kinds of  problems:

1.    Files become huge and the project must be partitioned in some way to allow design to continue; the files are large, slow, and cumbersome.

2.    Determining the changes within a file is still a manual management effort, replacing a red marker on drawings in drafting with notes in a 3D PDF or similar reviewing file. Traditionally, major changes at the construction document stage were not allowed because of their prohibitive cost. BIM and model management is supposed to eliminate or greatly reduce this problem. While parametric updates resolve issues of local changes, the coordination of different models and their derived data for schedules, analyses, and reports is still an important and growing  issue.

The long-mentioned but only recently realized capability of only exchanging the new, modified or deleted object instances in a file, eliminating the “chaff” of the nonmodified objects has now been brought out in a production environment, notably ArchiCAD’s Delta BIM server (more fully reviewed in Chapter 3, Section 3.5.3). Transferring only the changed objects and importing them, called an incremental update, greatly reduces the size of the exchange files, and allows for immediate identification and targeting of the change issues. This capability requires object identification and version control at the object level, usually provided by a timestamp. This capability will become increasingly important as BIM models grow. It will become a “must” feature on future releases of all systems, for coordination across multiple BIM   applications.

External Parameter Management

A capability explored in a number of innovative projects has been to control the geometric layout of a design based on control parameters (often a 3D grid) generated and defined in a spreadsheet. An example application of using a spreadsheet to control and coordinate geometry is presented in both the building core model in Chapter 5 and the Aviva Stadium case study project reviewed in Chapter 9, Section 9.1.

For certain types of projects, the ability to read from and write to spread- sheets provides a level of interoperability among different design tools. Suppose the equivalent parametric models can be built in two different modeling environments, say Rhino and Bentley, with the same parameters controlling the geometry.  Design explorations can be made in Rhino, generally a friendly but information-limited design tool, then the parameters updated in Bentley rchitecture, allowing the changes to be integrated in a BIM tool that might have cost or energy analysis capabilities. The spreadsheet provides an important level of geometric interoperability.

Another use of external spreadsheets of parameter lists is to exchange parametric objects by reference, rather than explicitly. The best-known exam- ple is steel structures. Steel handbooks, now in digital forms, carry the differ- ent standard profiles for structural steel, such as W18×35 or L4×4. These profile names can be used to retrieve profile, weight, and mass properties from the steel handbooks. Similar profiles are available for precast concrete prod- ucts, reinforcing bars, and some window manufacturer catalogs. If the sender and the receiver each have access to the same catalog, then they may send and retrieve the relevant information by reference (name) and the exchange is made by retrieving the appropriate catalog information and loading it into the appropriate parametric model for the part. This is a significant capability in many production areas.

Links to External Catalog  Files

Another important capability is to provide links to external files. The primary use of this capability today is to link products with their associated manuals for maintenance and operation, for later association with facilities operation and maintenance (O&M). Some BIM tools offer this capability and enhance their value as being a tool that can provide support during the O&M stage.

The functional capabilities outlined in this p are all important in assessing and selecting a BIM platform. They will be used later in this chapter when we assess the major BIM design  tools.