Alpha Version RELEASED today – May 29, 2008

Multi-Lat™ 2008 version 1.040108A

Alpha Version Release Notification

The Alpha version of Multi-Lat™ 2008 was released today. This is not a finished version – far from it. It is a work in progress and not intended to be used as a work product until it has been adequately carried through the entire Beta Program.

The Excel 2007 Workbook was delayed when a discussion was posted on the SEAINT Listservice (http://www.seaint.org click on the listservice choice in the left side of the web page to reach the subscribers page). While working on the spreadsheet software it became apparent that many engineers have been misinterpreting the base method that the seismic shear presents in both the IBC and ASCE 7-05. The default calculations for load cases is in Working Strength Design methods. The user must use the provisions of the ASCE 7-05 to decide to use the Allowable Stress Design (ASD) or Load and Resistance Factor Design (LRFD). This will, in most cases increase the lateral base shear that you evaluate closer to the base shear we used in the 97 UBC.

I have not yet finished this last part of Multi-Lat™ 2008 Alpha pending the next discussion on the need to consider an increased Redundancy Factor – Ρ (rho) and possibly the Over-strength factor – Ω ₀ (Omega). This last factor becomes more important when you consider using the simplified design methods of ASCE 7-05 Section 12.14.1.1.

I recently reviewed the information published in Donald Breyer’s book “Design of Wood Structures” sixth edition. I will be posting a discussion once I have some sketches together that we need to throw back and forth that Breyer brings up in Chapter 16 of his book. There are implications that most residential buildings in Seismic Design Category D, E and F will have some form of Vertical or Horizontal Irregularity that must be addressed unless the building is a simple block design where all walls stack (inside and exterior shear resisting elements). Please refer to the on-going discussion in the Weblog regarding Irregular Geometry and the introduction or the Over strength Factor – Ω ₀

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In the Code Simple feature published in Structural Engineer Magazine February 2008 edition by S.K. Ghosh and Susan Dowty, the last paragraph emphasizes the ambiguity in the code where it states:

“So what is the code user to do in this quagmire? The good news is that the problem has been solved for the user in the 2007 Supplement to the 2006 IBC. The Supplement has deleted the special seismic load combinations in 2006 IBC Section 1605.1. The section now simply directs the users to use Section 12.4.3 of ASCE 7-05, except that it clarifies: “With the simplified procedure of ASCE 7 Section 12.14, the overstrength factor load combinations of Section 12.14.3.2 of ASCE 7 shall be used.” Although supplements are typically not adopted by local jurisdictions, what the 2007 Supplement has done would be an advisable way to resolve the problem that exists with the 2006 IBC.” ( http://www.gostructural.com/article.asp?id=2605 )

Donald Breyer’s text takes the issue of Plan irregularity (vertical and horizontal) into much greater detail in Chapter 16 of the Sixth Edition. As Professor Ghosh points out, the “quagmire” does not actually disappear from most structures. Unless the home is a one story structures with no horizontal plan irregularity (including reentrant corners) where a prescriptive code such as International Residential Code most of us will find that some Vertical or Horizontal plan irregularity as noted in Table 12.3-1 and 12.3-2 will occur in most of our design. Whether or not the base shear is penalized by use of Ω ₀ depends upon the Seismic Design Category (SDC) and the Occupancy Category the structure conforms to permits (or not) in table 12.6-1. However, remember that the interpretation of Irregularity changed somewhat from what we were using in the 97 UBC on the West Cost until this year. For example, a Vertical Irregularity exists if the second floor shear wall does not align over the first floor shear wall. If there is transverse “jog”, the irregularity exists. If you recall in the 97 code the walls could be within 4′-0″ of the offset to still be in the same line of shear. Of course the engineer had to accommodate the design for potential tension and compression of the upper level walls and their connection to the framing in the diaphragm below. In this version of the code, if both walls are in the same line of shear but the upper level wall is in front of or behind the lower level wall a Vertical Irregularity exists and the base shear formula changes.

Another issue that I have not verified is the limitations on section 12.14.1 and table 12.6-1 to a maximum 2-story building where a setback or vertical irregularity (or horizontal irregularity occurs). To help you, an Irregularity worksheet was added to the workbook so that you can review the tables 12.3-1 and 12.3-2 as well as 12.6-1. Where Multi-Lat™ errs is on the side of conservative results.

Breyer states it very well on page 2.43 of Design of Wood Structures 6th edition where he states:

“ASCE 7 Sec. 12.14 is titled Simplified Alternative Structural Design Criteria for Simple Bearing Wall or Building Frame Systems. This section provides a simplified version of the equivalent lateral force procedure, for use on a limited scope of buildings. Use of the simplified procedure should result in roughly equivalent results. Because the scope of the buildings is limited, there are a number of checks in the general procedure, which do not need to be considered in the simplified procedure. ASCE 7 Sec. 12.14.1.1 provides a list of 12 scoping criteria that the building must meet in order to be designed using the simplified procedure. Among the 12 there is one that will be problematic for a number of wood-frame buildings. Item 11 says the simplified approach is not permitted in structures with system irregularities due to in-plane or out-of-plane offsets of lateral force resisting elements. An exception permits offsets in shearwalls in two story buildings of light-frame construction, provided detailing requirements are met. Because offsets in shearwalls from story to story are so common in wood-frame buildings, there are likely to be a good number that do not qualify for this procedure. For this reason this book addresses the equivalent lateral force procedure instead. “

Excel 2007 – Why?

This Alpha version is being released to all BT members but only those who are using Excel 2007 will be able to take advantage of the features. This version is Macro-enabled, but there are currently no macros prepared in the version (such as those expected to be used for automated printing.

Excel 2007 uses pre-defined style sheets that are embedded in the workbook to improve the appearance of the interface and the output of the printed version. It is possible to strip out the styles and make this XLS or compatible with Office 97-2003 and later with Sun Micro-systems® OpenOffice.Org Calc (free) software packages. The goal is to create an affordable tool that does not require the user to invest in additional spreadsheet investments. With this said, users of Excel 2007 will initially gain the most advantage in both user interface and readible output.

Protected Spreadsheets

I initially wanted to create a spreadsheet that was an open code to allow user’s to improve upon the software and to send the improvements back for inclusion in future releases. However, the truth is that in the last version of Multi-Lat™ ( written for the 97 UBC) I worked with many users who improved the software and then wanted to protect their work and competitive edge. With the exception of the initial release that included the Rigid Diaphragm Analysis improved by David Merrick, SE of Northern California, none of the other versions that were modified or changed and coordinated with me were re-submitted for the benefit of others.

The second reason is to protect the integrity of the conditional logic embedded in the workbook. We must, as a group, verify the structural accuracy and integrity of the spreadsheet results and protect it from change that can produce inaccurate output. This version is re-written from the ground up and the complexity of the conditional logic is discussed in this blog and where possible, is converted to a flow chart to simplify the path across the IBC and ASCE 7-05. Tables are protected from copyright infringement since the information is required to comply with the “law” but the tables as published in the IBC and ASCE 7-05 are protected by publication copyright laws. Therefore, only the information contained within the table necessary to publish this software becomes visible as input from pull-down menu choices. The tables are concealed to protect the ICC from those who might benefit from the use of the tables without purchasing the codes. I must warn the user that this spreadsheet software is not intended to replace the code but rather requires the user’s understanding of the information contained in both references (the 2006 IBC, ASCE 7-05 and the 2007 California Building Code).

Alpha Limitations

The alpha version will produce some useful information that can help reduce your time in calculations that you are currently doing manually. However, I want to warn you that you are checking this software for accuracy – especially to verify if the results of the logical conditions contained in the workbook produce similar results as you obtain manually. Be careful in how you use this workbook – it is not intended for project use at this time although I have taken particular care in checking my work and seeking to produce accurate results. I can not check all conditions and this is where your response is important. If the logic is even slightly wrong- for example if the conditional assumes a “greater than” rather than a “greater than OR equal to” – then the output will not be accurate for the condition it is being used and this will become a task that I will need to address before continuing with the next section of the Workbook.

This Alpha version may seem “lighter” than promised, but there is a great deal that is hidden, in partial work product or extensive tables that are not intended to be modified by the user. Macros are not yet functioning and the Hyperlink table of contents to easily move around the workbook is disabled.

In the Material Dead Load Section you may go to the worksheet that stores the material and unit weight. You are free to change this, but I would ask you to submit your changes to me so that I can compare the results to other Beta Users in order to change or add materials that I had not considered (and correct unit loads that you might consider significantly different).

Most of the input is self explanatory and I am working on a User’s Guide on the side (as time permits). It will be available in the final Beta either on this Weblog or as a separate download. You may only place your cursor where the cells are unlocked. The spreadsheet should seem more like a program than a spreadsheet but protection of the integrity of the conditional statements is extremely important.

Your mission, should you decide to accept…..:)

I am offer Multi-Lat™ in appreciation for your help in maintaining the accuracy and usefulness of the program. Therefore, I need your comments and suggestions – including constructive criticism. For example, if you don’t agree with the logical steps (each choice will display the code section that triggered the condition) let me know or provide a debate so others can convince me that I was mistaken or missed the mark. If you don’t like the colors, please give me some suggestions that you like to work with – especially if you do not use a color printer.

I need you to keep the comments coming

~ by structuralist on March 31, 2008.