Identification of Natural Frequencies and Dampings of In Situ Tall Buildings Using Ambient Wind Vibration Data

An accurate prediction for the response of tall buildings subject to strong wind gusts or earthquakes requires the information of in situ dynamic properties of the building, including natural frequencies and damping ratios. This paper presents a method of identifying natural frequencies and damping ratios of in situ tall buildings using ambient wind vibration data. Our approach is based on the empirical mode decomposition (EMD) method, the random decrement technique (RDT), and the Hilbert–Huang transform. Our method requires only one acceleration sensor. The noisy measurement of the building acceleration is first processed through the EMD method to determine the response of each mode. Then, RDT is used to obtain the free vibration modal response. Finally, the Hilbert transform is applied to each free vibration modal response to identify natural frequencies and damping ratios of in situ tall buildings. The application of the proposed methodology is demonstrated in detail using simulated response data of a 76-story benchmark building polluted by noise. Both the along-wind and across-wind vibration measurements have been illustrated. Simulation results demonstrate that the accuracy of the proposed method in identifying natural frequencies and damping ratios is remarkable. The methodology proposed herein provides a new and effective tool for the parametric identification of in situ tall buildings.     

Development of Energy-Efficient Concrete Buildings Using Recycled Plastic Aggregates

Recycled plastics (high-density polyethylene, polyvinyl chloride, and polypropylene) were used as coarse aggregates in concrete mixtures to alter and improve the thermal properties of buildings. Two similar retail buildings were designed and constructed in Lansing, Mich., one with normal concrete (control) and the other with high content of recycled mixed plastics. The thermal and energy performance of the two buildings were investigated and analyzed. Short-term (air tightness and infiltration, co-heating, lighting) and long-term monitoring were performed. The building simulation program SUNREL developed by the National Renewable Energy Laboratory (NREL) was employed to simulate the energy performance of the two buildings and to validate the experimental data. Both experimental and SUNREL program results showed that the recycled plastic concrete building exhibited higher levels of energy efficiency and comfort when compared with the normal concrete (control) building. Recycled plastic concrete in combination with energy-efficient building design techniques proved to be of tremendous value in lowering the cooling and heating loads of the buildings and also in enhancing the comfort level of the buildings.     

Field Probe for Measuring Thermal Resistivity of Soils

Estimation of thermal resistivity of soils is normally done in the laboratory with the help of a laboratory thermal probe. However, as naturally occurring soils consist of various size fractions, ranging from clay to gravel, this probe cannot be used efficiently for measuring their thermal resistivity. This necessitates fabrication of a field probe that can be used to measure thermal resistivity of a soil either in its remolded state or under in situ conditions. With this in view, efforts were made to develop a field probe that works on the principle of the transient method and is a magnified version of the laboratory probe developed by Rao and Singh in 1999. The results obtained have been validated using the findings of Van Pelt in 1976 and Johansen in 1975 for gravels and crushed rocks.     

Variations of Thermal Conductivity of Insulation Materials Under Different Operating Temperatures: Impact on Envelope-Induced Cooling Load

The thermal and energy performance of buildings depends on the thermal characteristics of the building envelope, and particularly on the thermal resistance of the insulation material used. The performance of the thermal insulation material is mainly determined by its thermal conductivity, which describes the ability of heat to flow across the material in the presence of a differential temperature. The value of the thermal conductivity of a particular material is subject to variation, due to changes in both moisture content and temperature. In reality, thermal insulation in buildings is exposed to significant and continuous temperature variations, due to varying outdoor air temperature and solar radiation. However, when calculating cooling loads or performing energy analyses for buildings, most designers, if not all, use published or manufacturer-supplied values of thermal conductivity, which are normally evaluated at 24°C according to the ASTM standards. Currently, many types of insulation materials are produced in Saudi Arabia, but not enough information is available to evaluate their performance under the prevailing climatic conditions. The objective of this paper is to present the results of a study that investigates the relationship between the temperature and thermal conductivity of various types of locally produced insulation materials. Additionally, the impact of thermal conductivity variation with temperature on the envelope-induced cooling load for a theoretically modeled building is quantified and discussed. Results are expected to clarify the issue of thermal conductivity dependence on temperature and lead to a more accurate assessment of the thermal and energy performance of buildings.     

Serviceability of Materials in the Tropics

With increasing complexity in the building construction trend and the advancement of building material technology, more building materials and substitutes have evolved and been adopted for use to function together in a building that is supposed to maintain its technical performance during its intended working life. Condition surveys of 450 buildings, face-to-face interviews, and workshops were conducted with industry specialists, to examine the behavior of materials used in facades and wet areas in tropical climates and their estimated costs of maintenance. This paper presents an indicative computational method for the durability of building materials for fa?ades and wet areas in the tropics. Total operations and maintenance costs of the identified materials are also included to provide suggestive maintenance expenditure over the materials’ service life. Natural stone was preferred as a more durable fa?ade material while ceramic and homogeneous tiles proved more economical for wet areas.     

IFC-Based Framework for Evaluating Total Performance of Building Envelopes

Evaluating the overall performance of buildings has emerged as a trend in building engineering in recent years. Several programs that evaluate building performance have been developed or are being developed in different regions of the world. The building envelope performance assessment tool was initiated at Concordia University based on the feedback received from manufacturers. After briefly introducing the development of the tool, this paper presents an integrated framework which applies information technology and the international standard Industry Foundation Classes (IFC) to ensure that the building envelope satisfies energy requirements as well as other requirements such as moisture and thermal performance, concurrently. The framework is designed to extract geometric and material layers’ data of a house from computer-aided design (CAD) drawings in IFC data model, link to performance evaluation applications, such as HOT2000 and MOIST3.0, and compare evaluation results with a set of criteria. To demonstrate the functionalities of this framework, a prototype system has been developed including a preprocessor that imports the building model from an IFC-compatible CAD application, an application integrator, and a postprocessor. Finally, a case study, which aims to validate this prototype system, is discussed in detail.     

Wind Environmental Conditions in Passages between Two Long Narrow Perpendicular Buildings

This paper presents wind tunnel measurements of pedestrian wind conditions in passages between various configurations of two long narrow perpendicular buildings in open country exposure. The investigated parameters are passage width, building height and wind direction. The measurements were made along the passage centerline. The aim of this paper is to provide more insight in the pedestrian wind conditions in these basic building configurations, to address some contradictory statements reported in the literature and to provide detailed experimental data for computational fluid dynamics (CFD) validation. The results show that the wind speed amplification factors in diverging passages are generally larger than in converging passages. It is also shown that the maximum wind speed amplification factors increase monotonically with decreasing passage width, contrary to some general building design guidelines proposed in the past for such building configurations. Significant issues concerning the use of the experimental data for CFD validation are also discussed.     

Four-Tube Probe for Velocity Measurement in 3D Flows

This paper presents the concept and development of a four-tube probe for the measurement of the three velocity components in 3D flows. The necessary calibration curves have been developed and are presented along with a procedure to use this probe. This probe is more convenient to use than the traditional five-tube probe and is believed to be useful for the measurement of the three components of velocity in 3D flows in the laboratory. It has already been used successfully in the measurement of the velocity field in a vertical slot fishway.     

Thermophysical properties of roll-compacted nickel sheet for high-density infrared sheet fabrication

This work is focused on the analysis of the high-density infrared (HDI) sheet fabrication process of powder compacts. Measurements of material properties and distribution of incident heat flux on processed powder sheet surfaces have been conducted with the aim of obtaining a complete set of data that can be used as input in computer simulation software. It was found that these materials exhibit significant anisotropy in thermal conductivity. Indirect measurements indicate that there are small variations in density across the thickness of the powder compacts. Temperature data were obtained from thermocouples placed on the backside of the sheet. The evolution of thermal profile during a static pulse was investigated by using a three-dimensional finite volume model. Numerical simulation results are very sensitive to the surface emissivity. Numerical simulation results agree very well with experimental results for the case in which no liquid pool was formed during HDI processing.     

Nonstationary hot wire method with silica-coated probe for measuring thermal conductivities of molten metals

The nonstationary hot wire method with a silica-coated probe has been developed to measure thermal conductivities of molten metals at high temperatures. Measurements were carried out on mercury and lead as test liquids. The thermal conductivities of liquid mercury ranged between 7.6 and 8.1 W/m K at temperatures between 273 and 293 K, and those of molten lead displayed constant values of about 15 W/m K at temperatures between 673 and 973 K. Factors affecting the thermal conductivity measurement using this method have been discussed. It has been concluded that the nonstationary hot wire method with an insulator-coated probe can be applied to various molten metals, as long as materials for probe coating are pertinent.     

Historic Building Stones and Flooding: Changes of Physical Properties due to Water Saturation

Natural stone is a common material in historic constructions. Flood events may directly affect surfaces of historic stone buildings. Since ashlars and stone sculptures often carry valuable cultural information, a more detailed knowledge about changes in physical properties due to water saturation is crucial for the assessment of their surface stability in case of flooding. Water saturation of stones leads to loss of mechanical strength and to expansion of volume (hydric dilatation). On the basis of data from literature, a rough scheme of vulnerability is suggested for different kinds of building stones. The majority of igneous and metamorphic rock types with dense crystalline structure are not vulnerable to flooding, whereas some types of pyroclastic rocks (tuffs) as well as clay-bearing sandstones are highly vulnerable. Detailed laboratory investigations on Elbe sandstone demonstrate the influence of petrographic features on material behavior due to water saturation. Results of laboratory tests are in good accordance to on-site observations made after the great summer flood in Dresden, Germany in 2002.     

Mars Soil Mechanical Properties and Suitability of Mars Soil Simulants

Determination of Mars soil mechanical properties will improve future lander mission success and provide narrower constraints for geomorphological modeling. A soil mechanics investigation was conducted wherein soil mechanical properties were determined by computer reconstruction of mass wasting features observed in photographs of Mars Exploration Rover landing sites and analysis of natural slope stability. Mars soil mechanical properties were compared with thermal inertia measurements and a correlation is presented. Tests with rovers and equipment for Mars surface exploration and various past laboratory experiments have incorporated a number of different Mars soil simulants. Standard laboratory measurements were conducted to characterize the shear strength, grain size distribution, and densities of various Mars soil simulants. From these measurements, the ability of a given simulant to appropriately represent the mechanical properties of in situ Mars soils was judged. Specific simulants are recommended for certain regions of Mars.     

High Strength Low Alloy (HSLA) Steels in Building Construction

Majority of the buildings,including industrial buildings,are constructed using either structural steel (plates and structural shapes) or deformed bar steel reinforced concrete.Such buildings,however,must be designed to be safe and serviceable during construction and during use and occupancy.These objectives can be easily achieved by the use of steels having superior mechanical properties,ductility,weldability,fire resistance,etc.Over the years,the steel industry has made improvements in steel making technologies resulting in high strength low alloy (HSLA) steels with superior steel properties well suited for building construction.First part of this paper presents the structural design considerations,and the constructional considerations associated with the building structures in general,and steel structures in particular.This second part of the paper looks at the acceptance criteria for HSLA steels for North American building codes and construction.The third part of the paper presents the structural properties of currently available HSLA steels for building construction.The discussion focuses on hot-rolled structural steel shapes as well as deformed steel bars for concrete reinforcement.The paper argues that Niobium microalloying is the key to achieving superior properties in such steels.     

Heat flux transducer measurement error: a simplified view

Heat flux transducers (HFTs) provide a simple and direct measurement of body heat exchange. Regrettably, HFTs perturb the heat flux at the measurement site, resulting in underestimations of the true heat flux. Equations to correct the discrepancy are available, but most require high-precision temperature measurements above and/or below the transducer and/or deep within the body tissues. Because this is not always feasible, the equations are of limited practical benefit. A theoretical basis for the magnitude of the correction factor in relation to the thermal resistances of the materials both above and below the HFT has been developed and has been verified experimentally. The theory is presented in a graph that can be used to drive the HFT correction factor directly or as a guide to know that heat flux was measured within a certain accuracy. This may obviate the use of complicated procedures and equations to perhaps needlessly apply a small correction factor to HFT data.     

Magnetic anisotropy predictions from texture measurements using a selected-depth technique

The correlation of textures with certain physical properties has been studied extensively for crystalline materials. Texture measurements have usually been performed using composite specimens. With a single measurement, these provide a through-thickness textural average. While this may be appropriate for the prediction of properties that are controlled by bulk characteristics (core loss, elastic modulus,etc.), the composite technique may not accurately predict properties that are controlled by the near-surface material volumes. This is especially true for rolled materials, which often possess through-thickness texture gradients. One such surface-sensitive property is magnetic permeability. In this case, the single composite measurement could be replaced by several measurements performed in the rolling plane at selected depths. Using available software, the unmeasured rims of pole figures can be accurately completed for harmonic orientation distribution function (ODF) calculation. This study consists of examples where the selected-depth technique was used for permeability and for core-loss predictions for a motor lamination steel. An example is provided showing how emphasis on near-surface textures improved the permeability prediction for a specimen possessing a texture gradient.     

Oxygen probes based on calcia-doped hafnia or calcium zirconate for use in metallic melts

Up to the present, fully or partially stabilized zirconia has been used as a solid electrolyte material in probes for the determination of oxygen in metallic melts. In the present study, the ionic conduction behavior of HfO₂ (CaO) solid solutions and the compound calcium zirconate CaZrO₂ have been investigated. Both polarization experiments and EMF measurements on oxygen concentration cells point out that these two highly refractory oxide materials are also most suitable solid electrolytes. Their use is particularly recommended for oxygen probe measurements in deoxidized steel melts where extremely high chemical stability and low partial electronic conductivity of the solid electrolyte is required. In the paper, properties such as crystal structure, free energy of formation, thermal expansivity, ionic and total electrical conductivity are summarized and compared for fully and partially stabilized ZrO₂, calcium zirconate CaZrO₃, HfO₂ (CaO), and ThO₂ (Y₂O₃) solid solutions.     

Design and Construction Challenges of a Federal Laboratory Building: A Case Study

This paper presents a case study regarding design and construction challenges of a federal laboratory building. The case study illustrates the successful collaboration of two federal agencies, General Services Administration (GSA) and Centers for Disease Control and Prevention (CDC). Creative methods were used to resolve complex design, construction, and budgetary issues. This paper describes lessons learned from a specific laboratory project on issues such as: A master plan and its role in locating secure laboratory buildings, site planning issues, contracting mechanisms, building security, energy, project development, design and construction excellence, and funding. Although CDC and GSA approved the release of this paper, the authors offer a disclaimer that the opinions and conclusions drawn in the papers are those of the authors, and are not necessarily shared by the CDC and GSA.     

Numerical Analysis of Neutron Moisture Probe Measurements

The neutron probe has proven to be an effective means for monitoring long term in situ soil moisture variations. However, it is difficult to experimentally correlate neutron probe data (i.e., neutron counts) with accurate estimates of absolute soil moisture content, particularly for unsaturated clay soils. In this paper, a numerical model based on multigroup neutron diffusion theory is employed to predict the distribution of neutron flux in a neutron probe system. The model discretizes the neutron energy spectrum into seven intervals, with energy-dependent diffusion coefficients and parameters for each energy interval. The finite element method is employed to solve the coupled seven-group neutron diffusion equations. It is demonstrated that the numerical results compare very well with both laboratory experimental results and field measurements. The theoretical approach to neutron probe calibration described herein offers significant time and cost savings over traditional calibration methods, and potentially opens up new applications for neutron probe monitoring.     

Coupled Use of Cone Tip Resistance and Small Strain Shear Modulus to Assess Liquefaction Potential

Resistance against earthquake-related liquefaction is usually assessed using relationships between an index of soil strength such as normalized cone tip resistance and the cyclic resistance ratio (CRR) developed from observed field performance. The alternative approach based on laboratory testing is rarely used, mainly because of the apprehension that laboratory results may not reflect field behavior since the quality of laboratory data is often compromised by sampling disturbance. In this study, a database of laboratory data obtained mainly from cyclic testing of frozen (undisturbed) samples and in situ index measurements from near sampling locations comprised of cone tip resistance, qc, and shear wave velocity, Vs, have been assembled. These data indicate that neither normalized cone tip resistance nor normalized shear wave velocity individually correlate well with laboratory-measured CRR. However, the ratio of qc to the small strain shear modulus, G0, relates reasonably with CRR via separate correlations depending on geologic age. The derived qc/G0-CRR relationships were also found to be consistent with earthquake field-performance case histories.