Thursday, August 28, 2008

New ISO standard for safe, long-lasting buildings and structures

ISO has published a new standard to help engineers, builders, and regulators to design structures that are safe and resistant to failure due to environmental and mechanical stresses, and to material degradation.

Buildings, civil engineering works, industrial structures, and their components should be conceived, constructed, inspected, maintained and repaired in such a way that, under foreseeable environmental conditions, they maintain their required performance during their design lives with sufficient reliability for the safety and comfort of users and the intended use of the structure.

ISO 13823:2008—General Principles on the Design of Structures for Durability specifies general principles and recommends procedures for the verification of the durability of structures subject to known or foreseeable environmental actions, including mechanical actions, causing material degradation leading to failure of performance. It will help to ensure reliability of performance throughout the service life of the structure.

This International Standard has the following objectives:

  • to improve the evaluation and design of structures for durability by the incorporation of building science principles into structural engineering practice, and
  • to provide a framework for the development of mathematical models to predict the service life of components of the structure.
Prof. A.M. Brandt, Chair of ISO/TC 98, Bases for Design of Structures, comments, "The general principles in the verification and design of structures and components for durability in this International Standard should be used whenever a minimum service life is required, for new structures as well as for the assessment of existing structures."

The standard is intended to serve a similar harmonization role that ISO 2394:1998, General Principles on Reliability for Structures, has had over the past 30 years for the verification and design of structures against failure due to mechanical stress, ranging from gravity to wind, snow, and earthquake.

The goal is to ensure that all analytical models are incorporated into the limit states method, the same as currently used for the verification and design of structures.

ISO 13823:2008 covers the following topics:
  • basic concept for verifying durability,
  • durability requirements,
  • design life of a structure and its components,
  • predicted service life, and
  • strategies for durability design.

This International Standard does not directly address sustainability for structures. Most considerations of sustainability, such as the choice of material as it affects waste and energy consumption, are outside its scope. But indirectly, durable structures improve the sustainability of infrastructure.

ISO 13823—General Principles on the Design of Structures for Durability, was developed by ISO technical committee ISO/TC 98, Bases for Design of Structures, Subcommittee SC 2, Reliability of Structures. For more information visit


Wednesday, August 20, 2008

What problem can you solve with 3 million 4 inch balls?

In order to protect a reservoir from sunlight 3 million black plastic balls are being added. The sunlight causes a reaction between the bromide and the chlorine resulting in the carcinogen bromate forming. The balls will not only block the sun but will be loads of fun for local kids! This was done at the Ivanhoe reservoir in LosAngeles county.


Thursday, August 14, 2008

A Formwork Formula: Tips For Success

Formwork—the temporary or permanent molds used to hold wet concrete until it cures—is a crucial element in concrete construction. Just as important is selecting the right type of formwork since that greatly affects the schedule, labor requirements, quality and total cost of a project.

Over the years, formwork molds have evolved from traditional job-built timber to pre-engineered systems composed of a combination of steel, aluminum, manufactured timber, plywood and plastics. These advancements in formwork molds have led to increased jobsite production and safety, with less labor, while producing a better finished product.

Formwork trends
Fewer than 15 years ago, approximately a dozen major formwork systems were readily available in the United States. However, over that short time period, several European forming companies have entered the domestic market, more than doubling the number of systems available.

The increase in competition is pushing innovations to a rate previously unseen in the industry. Thirty-year-old systems that have enjoyed wide use and popularity are being supplanted by new, modern systems that offer greater productivity and a higher quality results.

Walls—Presently, the most prevalent system in use for handset wall forming are steel-framed, wood-faced panels that require consumable ties at 2-feet-on-center and one connection per square foot. These are being replaced with larger, two-person handset systems that require less labor and eliminate consumable purchases because of reusable taper ties.

Gang forming has completely changed over the past 10 years. Older systems of steel-framed wood or steel-faced panels with double channel stiffbacks that connect with bolts/pins have been overtaken by clamp connection forms with wood or plastic form faces that provide tremendous labor savings in assembly and use. Assembly and reconfiguration of these standard systems to meet changing structure dimension happens very quickly, and also provides a consistent concrete finish.

Slabs—The use of fixed or adjustable wood posts, stringers and joists is still the most common method of shoring of slabs in the United States. This method ― passed down from generation to generation ― requires substantial labor. Because the posts are placed as close as 2-feet-on-center, construction sites become very congested.

A new construction method featuring engineered lumber and metal posts increases post spacing up to 5 feet by 10 feet and offers components that are systematic and reusable. This increased spacing allows for less material on site to form the same slab area. Less material means reduced handling requirements, less labor to set up and strip the formwork, lower transport costs, and an increase in overall job site productivity.

The current method for gang-forming slabs uses trusses or structural decks, which require a substantial amount of time for assembly and disassembly. Moreover, this method consumes an enormous amount of crane time, thus increasing the time for resetting a standard operating procedure. The customer must also purchase the plywood facing and sometimes replace it multiple times on the same project.

Because of the expense of setup and takedown, gang-forming slabs are used mostly on structures taller than 15 stories high. Smaller tables ― delivered to the job site fully assembled with plywood ― are becoming a better solution to these systems, especially for mid-rise buildings where gang-forming was previously not economical.

Another innovation that reduces job site crane time and formwork labor requirements is formwork-lifting elevators that mount to the exterior of a building, allowing all formwork to be cycled from floor to floor without the need for a crane. These table-lifting systems are used in conjunction with the smaller table method and also allow for other construction material including handset shoring, vertical formwork and reshores from below to cycle from floor to floor with a crane.

Read more (here)...



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